Multiple channel wireless communication system

ABSTRACT

A wireless transmission device for communicating a plurality of audio streams to remote devices comprises a plurality of inputs for receiving a plurality of digital audio streams, a combiner connected to the inputs for combining control codes and the received audio streams in a predetermined format to form a signal wherein the control codes for controlling the operation of a remote device equipped for processing the signal to extract the audio streams therefrom in accordance with the predetermined format, and a transmitter connected to the combiner to transmit the signal for reception by the remote device. The transmitter may include an infra-red light emitter for transmitting the signal as an infra-red light signal.

RELATED APPLICATIONS

[0001] This patent application claims the priority of provisional patentapplications serial number 60/340,744 filed on Oct. 30, 2001, serialnumber 60/347,073 filed on Jan. 8, 2002, and serial number 60/350,646filed on Jan. 22, 2002.

BACKGROUND OF THE INVENTION

[0002] This invention relates to wireless communication systems, andmore particularly to wireless audio systems for providing a plurality ofselectable audio signals from one or more sources to one or morelisteners in an automobile, airplane, or building.

[0003] Wireless audio systems currently known and available generallyinclude an audio source such as a tuner transmitting a signal to one ormore wireless headphones, wherein the signal carries a single stereochannel of audio data. To select a different channel of audio data,someone must operate the tuner to transmit the newly desired channel, atwhich point all wireless headphones receiving the signal will beginreproducing the new channel.

[0004] What is needed is an improved wireless communication systemincluding one or more wireless reception devices such as headphones,wherein the system offers multiple channels of audio and other data forindividual selection therebetween by each respective reception device.

SUMMARY OF THE INVENTION

[0005] In a first aspect, the present invention provides a wirelesstransmission device for communicating a plurality of audio streams toremote devices, comprising a plurality of inputs for receiving aplurality of digital audio streams, a combiner connected to the inputsfor combining control codes and the received audio streams in apredetermined format to form a signal wherein the control codes forcontrolling the operation of a remote device equipped for processing thesignal to extract the audio streams therefrom in accordance with thepredetermined format, and a transmitter connected to the combiner totransmit the signal for reception by the remote device.

[0006] In a further aspect, the wireless transmission device may furtherinclude an analog input for receiving an analog audio stream and aconverter connected to the analog input for converting the receivedanalog audio stream to a digital audio stream, the converter furtherconnected to the combiner to provide the converted digital audio streamto the combiner for combining with the control codes and the otherreceived audio streams. The transmitter may include an infrared lightemitter for transmitting the signal as an infra-red light signal.

[0007] In another aspect, the present invention provides a wirelessheadphone device comprising a receiver for receiving a wireless signalcontaining a plurality of digital audio streams combined with controlcodes according to a predetermined format, a decoder for extracting theaudio streams from the received signal in accordance with thepredetermined format and for responding to the control codes in thereceived signal to perform predetermined functions, a selector forselecting one of the extracted audio streams, a converter for convertingthe selected audio stream to an analog audio stream, an amplifier foramplifying the converted analog audio stream, and a loudspeaker forreproducing the amplified audio stream.

[0008] In a still further aspect, the wireless headphone device mayfurther include a photoreceptor for receiving the wireless signal as aninfrared light signal. The wireless headphone device may also include ademultiplexer to demultiplex the received signal and extract the audiostreams from the demultiplexed signal.

[0009] These and other features and advantages of this invention willbecome further apparent from the detailed description and accompanyingfigures that follow. In the figures and description, numerals indicatethe various features of the invention, like numerals referring to likefeatures throughout both the drawings and the description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a block diagram of wireless headphone system 10 inaccordance with the present invention;

[0011]FIG. 2 is a block diagram of wireless headphone system 10 using ananalog signal combining configuration;

[0012]FIG. 3 is a block diagram of one embodiment of a data streamformat used in a wireless headphone system according to the presentinvention, such as wireless headphone system 10 depicted in FIGS. 1 and2;

[0013]FIG. 4 is a block diagram schematic of one embodiment of areceiver or headset unit according to the present invention, such asheadset receiver unit 14 depicted in FIG. 1;

[0014]FIG. 5 includes top and front views of one embodiment ofmulti-channel headphones for use in system 10;

[0015]FIG. 6 depicts a functional block diagram of transmitter apparatus500 according to the present invention;

[0016]FIG. 7 depicts a hardware block diagram of encoder 626 oftransmitter apparatus 500 of FIG. 6;

[0017]FIG. 8 is a functional block diagram of clock and clock phasingcircuitry 628 of transmitter apparatus 500;

[0018]FIG. 9 is a functional block diagram of input audio conversionmodule 622 of transmitter apparatus 500;

[0019]FIG. 10 is a functional block diagram of IR module emitter 634 oftransmitter apparatus 500;

[0020]FIG. 11 depicts a configuration of transmission data input buffersfor use with transmitter apparatus 500;

[0021]FIG. 12 depicts a digital data transmission scheme according tothe present invention, that may be used with transmitter apparatus 500;

[0022]FIG. 13 depicts a functional block diagram of receiver apparatusor headset unit 700 according to the present invention, that may be usedin conjunction with a transmitter apparatus such as transmitterapparatus 500;

[0023]FIG. 14 is a functional block diagram of primary receiver 702 ofreceiver apparatus 700;

[0024]FIG. 15 is a functional block diagram of IR receiver 714 ofreceiver apparatus 700;

[0025]FIG. 16 is a functional block diagram of data clock recoverycircuit 716 of receiver apparatus 700;

[0026]FIG. 17 is a functional block diagram of DAC and audio amplifiermodule 722 of receiver apparatus 700;

[0027]FIG. 18 is a functional block diagram of secondary receiver 704 ofreceiver apparatus 700;

[0028]FIG. 19 is a diagram of a vehicle 800 equipped with communicationsystem 801 according to the present invention;

[0029]FIG. 20 is a diagram of another vehicle 800 equipped withcommunication system 801 having additional features over that shown inFIG. 19;

[0030]FIG. 21 is a diagram of vehicle 900 equipped with communicationsystem 901 according to the present invention; and

[0031]FIG. 22 is a diagram of a vehicle 988 equipped with communicationsystem 991 according to the present invention; and

[0032]FIG. 23 is a diagram of a building 1010 equipped with acommunication system 1000 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Referring to FIG. 1, one embodiment of a wireless communicationsystem according to the invention is wireless headphone system 10 thatincludes transmitter subsystem 12 that communicates with headset unit 14via infra-red (IR) or radio frequency (RF) signals 16, preferably aformatted digital bit stream including multi-channel digitized audiodata, calibration data as well as code or control data. The data beingtransmitted and received may comply with, or be compatible with, anindustry standard for IR data communications such as the Infra Red DataAssociation or IRDA.

[0034] Transmitter subsystem 12 IR transmitter section 18 including IRtransmitter 20, such as an infra-red light emitting diode or LED, drivenby an appropriate IR transmitter driver 22 receiving digitized audiodata from one or more digital signal processors, or DSPs, such as DSPencoder and controller 24, 27, 28 and/or 30. The digital data streamprovided by IR transmitter section 18 is preferably formatted inaccordance with any one of the proprietary formats described hereinbelow with reference to FIGS. 3, 10 and 16.

[0035] The digitized audio data may be applied to IR transmitter driver22 from a plurality of such DSP encoder and controllers that arecombined in signal combiner/multiplexer 32 that may be separatelyprovided, combined with IR transmitter section 18 or combined with DSPencoder and controller 24 in master controller 26. Master controller 26may be included within a first audio device, such as audio device 34,provided as a separate unit or included within IR transmitter section18.

[0036] In a system configuration in which master controller 26 isincluded within audio device 34, wireless headphone system 10 includingaudio device 34, IR transmitter section 18 and headset unit 14 mayadvantageously serve as a base or entry level system suitable for use asa single channel wireless headphone system that, in accordance with theproprietary formats described herein below with regard to FIGS. 3, 10and 16 may be easily upgraded for use as a multi-channel wirelessheadphone system. For illustrative purposes, audio device 34 is depictedin FIG. 1 as including audio stage 36, having first and second audiosources such as line 1 source 38 and line 2 source 40 each connected tostereo processing circuitry such as stereo channel 1 circuitry 42, theoutput of which is applied to master controller 26. Audio device 34thereby represents any audio source including mono and stereo radios, CDand cassette players, mini-disc players, as well as the audio portionsof electronic devices that provide other types of signals such ascomputers, television sets, DVD players and the like.

[0037] Whether included as part of an initial installation, or laterupgraded, a second audio source, such as MP3, WMA, or other digitalaudio format player 44, may be included within wireless headphone system10 to provide a second channel of stereo audio signals. In particular,MP3 player 44 may conveniently be represented by audio stage 46 thatprovides line 3 source 48 and line 4 source 50 to stereo channelcircuitry 52, the output of which may be a line out, speaker out orheadphone out port. As shown in FIG. 1, the output of stereo channelcircuitry 52 may be applied to DSP encoder and controller 27 forcombining in signal combiner/multiplexer 32 of master controller 26included within audio device 34. In this manner, an unmodifiedconventional stereo audio source such as MP3 player 44 may be added towireless headphone system 10 by use of an add on DSP device such as DSPencoder and controller 27.

[0038] Alternately, a DSP device included within an audio source forother purposes, such as related to the production of a digitized audiosignal, may be programmed to provide the control and formatting requiredfor providing an additional channel of data for wireless headphonesystem 10. In particular, new unit add in device 54 is shown as anexemplar of an audio source in which an included DSP has been programmedfor compatibility with the proprietary format described herein belowwith regard to FIG. 3. Device 54 generally includes line 5 source 56 aswell as line 6 source 58, both connected through stereo channelcircuitry 60 to DSP encoder and controller 28 for application to signalcombiner/multiplexer 32.

[0039] Similarly, an analog audio device may be included in wirelessheadphone system 10 by use of a legacy adapter, such as legacy adapter62. Legacy adapter 62 is illustrated as including line 7 analog audioinput 64 and line 8 analog audio input 66 both connected to stereochannel circuitry 68 for application to DSP encoder and controller 30.It should be noted that any one of the audio inputs designated as lines1 through 8, may be paired as stereo input lines, used singly asseparate monaural inputs, or in any other convenient combinations ofstereo and mono inputs or as part of a more complex audio format, suchas a home theater 5.1 or 7.1 system. Any one or more of lines 1 through8 may also be used to transmit non-audio data, as described in moredetail elsewhere herein.

[0040] As depicted in FIG. 1, wireless headphone system 10 may includeone or more digital audio sources and may also include one or moreanalog audio sources. As shown, transmitter subsystem 12 may include asingle digital signal combiner, such as signal combiner/multiplexer 32,fed by digital signals from each of a plurality of DSPs, such as DSPencoder and controllers 24, 27, 28 and 30. An alternate configuration oftransmitter subsystem 12 using analog signal inputs will be describedbelow in greater detail with respect to FIG. 2.

[0041] Still referring to FIG. 1, IR transmitter 20 in IR transmittersection 18 produces a digital bit stream of IR data, designated as IRsignals 16, from a convenient location having a direct line of sightpath to IR receiver 70 in headset receiver unit 14. In a home theaterapplication, IR transmitter 20 might conveniently be located at the topof a TV cabinet having a clear view of the room in which the listenerwill be located. In a vehicular application, IR transmitter 20 could belocated in a dome light in the center of the passenger compartment, ormay be a separate component mounted at a desirable and practicablelocation (such as near the dome light). In a larger area in whichmultiple headset receiver units 14 are to be driven by the same IRtransmitter 20, IR transmitter section 18 may include a plurality of IRtransmitters 20 each conveniently located to have a direct line of sightpath to one or more headset receiver units 14. In other embodiments, asdescribed elsewhere with regard to FIG. 17, IR transmission repeatersmay be provided to relay the digital bit stream transmitted by a singletransmitter 20 over longer distances or around obstacles that mayotherwise block the direct line(s) of sight from transmitter 20 to anyone or more of headset receiver units 14.

[0042] In many applications, the output of IR receiver 70 mayconveniently be processed by IR received signal processor 72. In eitherevent, after being received, IR signals 16 are then applied to decoder74, containing a clock, de-multiplexer, and controller, for processingto provide separate digital signals for stereo channels 1-4 to beapplied to DSP 76 for processing. DSP 76 may conveniently be amultiplexed DSP so that only a single DSP unit is required. Alternately,a plurality of DSP units or sub units may be provided.

[0043] The stereo audio channels 1-4 may conveniently each be processedas individual left and right channels, resulting in channels 1L, 2R, 2L,2R, 3L, 3R, 4L and 4R as shown. It should be noted, as discussed abovethat each of these audio channels may be used as a single monauralaudio, or data channel, or combined as shown herein to form asub-plurality of stereo channels. The resultant audio channels are thenmade available to switching selector 78 for selective application towireless headphone headset earphones, generally designated as headphones80.

[0044] In general, switching selector 78 may be conveniently used by thelistener to select one of stereo channels 1-4 to be applied toheadphones 80. Alternately, one or more of the stereo channels can beused to provide one or two monaural channels that may be selected by thelistener, or in specific circumstances automatically selected upon theoccurrence of a particular event. In the event headphones 80 areequipped to receive four (or any other number of) stereo audio channelsbut a lesser number of channels are available for transmission by audiodevice 34, the number of actual channels being transmitted may beincorporated into the digital bit stream of signals 16, and theheadphones may then allow a user to select only those channels that areavailable (e.g. if only two channels are being transmitted, the userwould only be able to toggle between these two channels, without havingto pass through two or more “dead” channels).

[0045] For example, switching selector 78 may be configured to permitthe listener to select one of three stereo channels, such as channels1-3, while stereo channel 4L may be used to provide a monaural telephonechannel and channel 4R may be used to provide an audio signal such as afront door monitor or a baby monitor. In the case of a baby monitor, forexample, switching selector 78 may be configured to automaticallyoverride the listener's selection of one of the stereo channels toselect the baby monitor audio whenever the audio level in the babymonitor channel exceeds a preset level. Further, a fixed or adjustabletime period after the audio level in the baby monitor channel no longerexceeds the preset level, switching selector 78 may be configured toautomatically return to the stereo channel earlier selected by thelistener.

[0046] Alternately, stereo channels 1-3 may be utilized to provide anaudio format, such as the 5.1 format used for home and professionaltheaters. In this type of format, a first stereo channel is used toprovide a front stereo sound source located left and right of the videobeing displayed. Similarly, a second stereo channel may be used toprovide a rear stereo sound source located left and right behind thelistener. A so-called fifth channel may be a monaural channel providinga non-stereo sound source located at a center position between the leftand right front stereo sources. A further monaural channel, representingthe so-called “.1” channel, may conveniently be a low frequency wooferor subwoofer channel whose actual location may not be very critical as aresult of the lower audio frequencies being presented. Similarly, stereochannels 1-4 may be utilized to provide audio in the so-called 7.1 audioformat.

[0047] Headphones 80 may conveniently be a pair of headphones speakersmounted for convenient positioning adjacent the listener's ears,particularly for use with wireless headphone system 10 configured forpermitting user or automatic or override selection of a plurality ofstereo or monaural channels. Headphones 80 may be used in thisconfiguration to present audio to the listener in a format, such as the5.1 format, by synthesis. For example, the center channel of the 5.1format may be synthesized by combining portions of the front left andright channels.

[0048] Alternately, as described below with respect to FIG. 5, alternateconfigurations of headphones 80 may be used to provide a more desirablerendition of a particular format by providing a plurality of pairs ofheadphone speakers mounted in appropriate positions adjacent thelistener's ears. For example, a first pair of speakers may be positionedin a forward position to reproduce the front left and right channels andto synthesize the center channel, a second pair of speakers may bepositioned in a rearward position to reproduce the rear left and rightchannels, with a resonant chamber mounted to a headband supporting thespeakers is used to provide the subwoofer (.1) channel.

[0049] Decoder 74 may also be used to produce control signals used forproviding additional functions. For example, control signals may beincorporated into the digital bit stream transmitted by audio device 34for error checking, power saving, automatic channel selection, and otherfeatures as described elsewhere herein. In addition to audio signalsprovided to DSP 76, decoder 74 may also be used to provide power controlsignal 82 for application to battery system 84. In particular, inresponse to the decoding of a code contained in the proprietary formatsdiscussed elsewhere, decoder 74 may provide a signal maintaining theapplication of battery power from battery system 84 to wirelessheadphone system 10. Thereafter, when the coded signal has not beenreceived for an appropriate time period, battery power would cease to beapplied to system 10 to provide an automatic auto-off feature that turnsoff system 10 to preserve battery power when the sources of audiosignals, or at least the formatted signals, are no longer present. Thisfeature can conveniently be used in an application in which system 10 isused in a car. When the ignition of the car has been turned off, thepower applied to headset receiver unit 14 from battery system 84 isstopped in order to preserve battery life. As discussed elsewhere, theautomatic auto-off feature may also be invoked when an error checkingfeature detects a predetermined number of errors.

[0050] Referring now to FIG. 2, in an alternative embodiment transmittersubsystem 13 may be configured with a single DSP for digitizing audiosignals that is programmed to provide signal combining and formatcontrol functions. In particular, the input to IR transmitter section 18may be provided directly by a properly configured DSP encoder andcontroller 24 that receives as its inputs, the analog audio signal pairsfrom stereo channels 1, 2, 3 and 4 provided by stereo integratedcircuits, or ICs, 42, 52, 60 and 68, respectively. The invention is notlimited to the use of a DSP and any practicable means for performing thefunctions herein described, including any other electronic circuit suchas a gate array or an ASIC (application specific integrated circuit)also may be employed and is within the ambit of the invention. For easeof understanding, however, the term DSP is used throughout thisspecification.

[0051] The source of stereo inputs for stereo channel circuitry 42 inaudio stage 36 may conveniently be line 1 source 38 and audio stage 36.The source of stereo input for stereo channel circuitry 52 in MP3 player44 may be line 3 source 48 and line 4 source 50, provided by audio stage46. Similarly, the sources of stereo input for stereo channel circuitry60 and 68 in new unit add in device 54 and legacy adapter 62 may be line5 source 56 and line 6 source 58 as well as line 7 analog audio input 64and line 8 analog audio input 66, respectively. It is important to notethat all four stereo sources may be combined to provide the requiredaudio signals for a complex format, such as 5.1, or one or more of suchstereo channels can be used as multiple audio channels.

[0052] Referring now to FIG. 3, the format or structure of IR signals 16is shown in greater detail. IR signals 16 form a bit stream of digitaldata containing the digitized audio data for four stereo channels, aswell as various calibration and control data. In one embodiment, IRsignals 16 are an uncompressed stream of digital data at a frequency orrate of at least 10.4 MHz. Pulse position modulation (PPM) encoding ispreferably used. This encoding increases the power level of pulsesactually transmitted, without substantially increasing the average powerlevel of the signals being transmitted, by using the position of thepulse in time or sequence to convey information or data. This powersaving occurs because in PPM encoding the same amount of informationcarried in a pair of bits at a first power level in an unencoded digitalbitstream may be conveyed by a single bit used in one of four possiblebit positions (in the case of four pulse position modulation, or PPM-4,encoding). In this way, the power level in the single bit transmitted inpulse position encoding can be twice the level of each of the pair ofbits in the unencoded bitstream while the average power level remainsthe same.

[0053] As shown in FIG. 3, IR signals 16 include a plurality oftransmitted signals (or packets, as described elsewhere herein) 86separated from each other by gap 100 that may conveniently simply be a16 bit word formed of all zeros. Gap 100 is useful to convey clockinginformation for synchronizing the receiver decoding to the clock rate ofthe transmitter, as described below in greater detail with respect toFIG. 4.

[0054] Transmitted signals or packets 86 may conveniently be partitionedinto two sections, header section 87 and data section 88, as shown. Datasection 88 may conveniently be composed of 25 samples of each of the 8audio data streams included in the four stereo signals being processed.For example, data section 88 may include word 103 representing thesampled digital output or stereo channel 1, left while word 104represents the sampled digital output of stereo channel 1, right,followed by representations of the remaining 3 stereo channels. Thisfirst described group of 8 digital words represents a single sample andis followed by another 24 sets of sequential samples of all 8 audiosignals.

[0055] In this example, each data section 88 includes 400 digital wordsto provide the 25 samples of audio data. If the data rate of the analogto digital, or A/D, conversion function included within DSP encoder andcontroller 24 shown in FIG. 1 is 16 bits, the first 8 bit word for eachchannel could therefore represent the high bit portion of each samplewhile the second 8 bit word could represent the low bit portion of thesample.

[0056] Referring now also to FIG. 1, if switching selector 78 isoperated to select a particular monaural or stereo channel, such aschannel 3, left, the known order of the samples may be utilized toreduce the energy budget of headset receiver unit 14. In particular,digital to analog (D/A) conversions may be performed during each datasection 88 only at the time required for the selected audio or stereochannels such as channel 3, left. In this manner, because the D/Aconversions are not being performed for all 8 monaural or 4 stereochannels, the power consumed by the D/A conversions (that are typicallya substantial portion of the energy or battery system budget) may besubstantially reduced, thereby extending battery and/or battery charge,life.

[0057] The organization of data block 92 described herein may easily bevaried in accordance with other known data transmission techniques, suchas interleaving or block transmission. Referring specifically to FIG. 3,in one embodiment each transmitted packet 86 may include header section87 positioned before data section 88. Each header section 87 may includeone or more calibration sections 101 and control code sections 102. Ingeneral, calibration sections 101 may provide timing data, signalmagnitude data, volume and/or frequency data as well as control datarelated, for example, to audio format or other acoustic information.Control code sections 102 may include information used for errordetection and/or correction, automatic channel selection, automaticpower-off, and other features of system 10. Another preferred embodimentis described elsewhere herein with reference to FIG. 12.

[0058] In particular installations, desired acoustic characteristics orthe actual acoustic characteristics of the installed location oftransmitter subsystem 12 may be synthesized or taken into account forthe listener. For example, the relative positions including azimuth anddistance of the various sound sources or speakers to the listener, in aparticular concert hall or other location, may be represented in thecalibration data so that an appropriate acoustic experience related tothat concert hall may be synthesized for the listener using headsetreceiver unit 14 by adjusting the relative delays between the channels.Such techniques are similar to those used to establish particular audioformats such as the 5.1 format.

[0059] Alternately, undesirable acoustic characteristics, such as thehigh pitched whine of an engine, or low pitched rumble of the road, thatmay penetrate the acoustic barrier of headphones 80 may be reduced oreliminated by proper use of the calibration data. This synthesis orsound modification may be controlled or aided by information incalibration portions or IR signals 16, such as calibration sections 101,and/or controlled or adjusted by the listener by proper operation ofswitching selector 78, shown in FIG. 1.

[0060] Similarly, the acoustic experiences of different types or stylesof headphones 80 may be enhanced or compensated for. Conventionalheadphone units typically include a pair of individual speakers, such asleft and right ear speakers 81 and 83 as shown in FIG. 1. A more complexversion of headphones 80, such as multi-channel headphones 118 describedbelow in greater detail with respect to FIG. 5, may benefit fromcalibration data included in calibration sections 98.

[0061] Techniques for adjusting the listener's acoustic experience maybe aided by data within calibration sections 101, and/or by operation ofswitching selector 78, as noted above, and also be controlled, adjustedor affected by the data contained in control code section 102. Controlcode data 102 may also be used for controlling other operations ofsystem 10, such as an auto-off function of battery system 84, errordetection and/or correction, power saving, and automatic availablechannel selection.

[0062] Referring now to FIG. 4 and 1, IR data in processed IR packets86, such as data section 88, may conveniently be applied to DSP 76, viadecoder 74, for conversion to analog audio data. IR data in headersection 87 may be further processed by other circuits, convenientlyincluded within or associated with decoder 74, for various purposes.

[0063] For use in an auto-off function, the portion of the IR dataprocessed by IR received signal processor 72 including control codesection 102 may be applied to code detector 106 to detect the existenceof a predetermined code or other unique identifier. Upon detection ofthe appropriate code, delay counter 108 may be set to a predetermineddelay, such as 30 seconds. Upon receipt of another detection of theselected code, delay counter 108 may then be reset to the predetermineddelay. Upon expiration of the predetermined delay, that is, uponexpiration of the predetermined delay with recognition of thepre-selected auto-off control word, a signal may be sent to kill switch110 that then sends power control signal 82 to battery system 84 to shutoff headset unit 14.

[0064] In operation, the above described procedure serves to turn offthe battery power for headset unit 14 unless an appropriate code signalhas been recognized within the previous 60 seconds. The auto-offfunction may therefore be configured to turn off battery power 60seconds (or any other predetermined period) after the cessation ofaccurate IR data transmissions by transmitter subsystem 12. As describedelsewhere, system 10 may incorporate error detection methods. In such anembodiment, the auto-off function may also be configured to turn offbattery power after a predetermined number and/or type of errors hasbeen detected. This approach provides an advantageous auto-off functionthat may be used to save headset battery power by turning off theheadphones a predetermined period after a radio, or other transmitter,in an automobile is turned off, perhaps by turning off the ignition ofthe car, or alternatively/ additionally when too manytransmission/reception errors have degraded audio performance to anunacceptable level. Headset unit 14 may also be configured to only powerdown upon detection of too many errors, wherein all processing ceasesand is reactivated at predetermined intervals (e.g. 30 seconds) toreceive a predetermined number of packets 86 and check for errors inthese received packets. Headset unit 14 may further be configured toresume full, constant operation after receiving a preselected number ofpackets 86 having no, or below, a preselected number of errors.

[0065] In an advantageous mode, kill switch 110 may also be used toprovide an auto-on function in the same manner by maintaining the powerapplied to IR received signal processor 72, delay counter 108 and codedetector 106 if the power required thereby is an acceptable minimum.Upon activation of an appropriate signal source as part of transmittersubsystem 12, the predetermined code signal may be detected and powercontrol signal 82 sent to battery system 84 to turn on the remainingunpowered systems in headset receiver unit 14.

[0066] Referring again to FIGS. 1 and 4, one important task inmaintaining proper operation of system 10 is to maintain synchronizationbetween the operations, particularly the sampling and/or A/D operationsof transmitter subsystem 12 and the decoding and related operations ofheadset receiver unit 14. Although synchronization may be maintained inseveral different ways, it has been found to be advantageousparticularly for use in a system (such as system 10) including apossible plurality of battery powered remote or receiver units (such asheadset units 14) to synchronize the timing of the operations of headsetreceiver units 14 to timing information provided by transmittersubsystem 12 and included within IR signals 16 to assure that thesynchronization was accurately achieved for multiple receiver units thatmay be replaced or moved between automobiles from time to time.

[0067] As shown in FIG. 4, IR data is applied from IR received signalprocessor 72 to synch detector 112 that may conveniently detect gap 100by, for example, detecting the trailing edge of data section 88 in aparticular transmitted packet 86 and, after an appropriate pre-selecteddelay or gap, detect the leading edge of header section 87 of asubsequent transmitted packet 86. Simple variations of this sync signaldetection may alternately be performed by synch detector 112 bycombining information related to the trailing edge, gap length and/orexpected data content such as all 1's or all 0's or the like and theactual or expected length of the gap and/or the leading edge.

[0068] Upon detection of appropriate synchronization data, sync detector112 may then maintain appropriate clocking information for headsetreceiver unit 14 by adjusting a clock or, preferably, maintainingsynchronization updating a phase lock loop circuit (or PLL), such as PLL114. The output of PLL 114 may then be applied to DSP 76 forsynchronizing the decoding and/or sampling of the IR data, for example,by controlling the clock rate of the D/A conversion functions of DSP 76.The resultant synchronized signals are then applied by switchingselector 78 to headphones 80. Applicants have found that without suchsynchronization, the audio quality of the sounds produced by headphones80 may be seriously degraded.

[0069] Another function that may be provided by decoder 74 includesupdating the operation of headset receiver unit 14. In particular, uponrecognition of an appropriate update code by code detector 106, the datain data section 88 from one or more subsequent transmitted signals orpackets 86 may be applied by code detector 106 to an appropriate memoryin headset receiver unit 14, such as rewritable memory 116. The datastored in memory 116 may then be used to control subsequent operationsof headset receiver unit 14 by, for example, decoder 74.

[0070] The update function described above with respect to FIG. 4 may beused to revise or update headset receiver unit 14 for operating modesthat vary the processing of data in multiple channel format, such asvariations in the 5.1 or 7.1 audio format. Other uses of the updateformat may be in automatically selecting the language or age appropriateformat used on various audio channels to control what is provided to aparticular listener.

[0071] For example, system 10 may be used in a museum to provideinformation, in audio format, for one or more exhibits. Before aparticular headset receiver unit 14 is provided to, or rented by, amuseum visitor, that headset unit might be programmed by use of theupdate format to provide age appropriate audio for the listener to beusing the headset unit.

[0072] Alternately, the updating may be performed upon rental of aheadset unit to correspond to the audio services to be provided. Aparticular headset might be programmed to automatically activate uponreceipt of an audio signal of a sufficient magnitude to indicateproximity to the exhibit to be described. One headset might beprogrammed to provide audio only for exhibits in a certain collectionwhile other headsets might be programmed to receive all related audio.This programming or updating may easily be performed at the time ofrental or other distribution for each headset.

[0073] Another use of the updating or programming function is to permitthe reprogramming of a larger number of headsets at the same time. Forexample, continuing to use the museum exemplar, a paging system,emergency or other notification system may be implemented with theupgrade function so that museum patrons with a selected code in theirheadset, or all such patrons, may be selectively paged or notified ofspecified information, such as museum closing times or the procedure tofollow upon declaration of an emergency such as a fire. In this way,such information may be provided in real time, from a simple telephoneor paging interface, by controllably switching the audio produced in oneor more selected headphones rather than by altering the audio beingnormally produced.

[0074] Another example of the use of the upgrade function might be tochange codes that permit operation of the headphones, or relatedequipment, to prevent stealing or tampering with the headphones.Headphones being improperly removed from a listening chamber, such as avehicle, may be programmed to issue a warning, to the listener or toothers, upon passing through an exit. In order to prevent tampering withthe headsets to foil such operations, the codes may be randomly orfrequently changed.

[0075] A further use of the upgrade function is to permit headphoneunits to be sold or provided for use at one level and later upgraded toa higher level of operation. As one simple example, multi-channelheadphones may be distributed without coding required to perform multichannel operation. Such headphones, although desirable for singlechannel operation, may then temporarily or permanently upgraded forhigher performance upon payment of an appropriate fee.

[0076] Referring now to FIG. 5, top and front views of multi-channelheadphones 118 use with system 10 are depicted in which left earphonesystem 120 and right earphone system 122 are mounted on head band 124that is used to position the earphones on the listener's head. Each ofthe earphone systems includes a plurality of speakers, such as frontspeaker 126, center speaker 128 and rear speaker 130 as designated onright earphone system 122 together with effective aperture 132 andeffective audio paths 134.

[0077] The apparent distances along effective audio paths 134 fromspeakers 126, 128 and 130 to effective aperture 132 in each earphone arecontrolled to provide the desired audio experience so that both theapparent azimuthal direction and distance between each speaker as asound source and the listener is consistent with the desired experience.For example, audio provided by speakers 126 and 128 may be provided atslightly different times, with different emphasis on the leading andtrailing edges of the sounds so that an apparent spatial relationshipbetween the sound sources may be synthesized to duplicate the effect ofhome theater formatted performances. Although the spatial relationshipsfor some types of sounds, like high frequency clicks, may be easier tosynthesize than for other types of sounds, the effect of even partialsynthesis of spatial sound relationships in a headset is startling andprovides an enhanced audio experience.

[0078] In addition to the speakers noted above for use in stereo andmultiple channel stereo formats, a low frequency, non-directionalmonaural source, such as sub woofer 134, may be advantageously mountedto headband 124 to enhance the user's audio experience.

[0079] With reference now to FIG. 6, in an alternative configuration ofan audio transmission device according to the invention, transmissiondevice 500 includes single DSP 600 may receive four digitized audioinput streams 602, 603, 604, 605 multiplexed by two multiplexers 606,608 into two signals 610, 612 for input into direct memory access (DMA)buffers DMA0 614 and DMA1 616 connected to serial ports 613, 615 of theDSP 600. Audio streams 602-605 may be digitized by analog-to-digitalconverters (ADCs) 618, 619, 620, 621 located for example in audiomodules 622, 623, 624, 625 shown in FIG. 7. Audio device 34 and MP3player 44 of FIG. 1 are typical examples of such audio modules. As notedabove with respect to FIG. 1, audio devices utilizing multiple analoginputs provided to a single ADC, as well as multiple digital inputs thatare provided directly to multiplexers such as multiplexers 606, 608, maybe used.

[0080] Referring to FIG. 7, the data multiplexing circuitry of audiotransmission device 500 combines two channels of digitized data 602, 603and 604, 605 into one serial data stream 610, 612 respectively. The datastream slots for two differently phased digital audio stereo pairs (twostereo pairs) 610, 612 are combined to create one constant digital datastream 633. The left/right clocking scheme for the audio modules,described in greater detail elsewhere herein, is configured such thattwo stereo channels (four analog audio input lines) share one data line.Outputs 602, 603 and 604, 605 of in-phase ADCs 618, 620 and 619, 621 aremultiplexed with the 90 degrees phase shifted data. The higher orderedchannels (Channels 3 and 4) are clocked 90 degrees out of phase of thelower channels (Channels 1 and 2). This allows two channels pairs(Channel 1 left and right and channel 3 left and right) to share asingle data line. Two sets of serial digitized audio data are input toDSP 600. Both odd numbered channels are on the same serial line and botheven numbered channels are on the same serial line. Clock and clockphasing circuitry 628 provides the input data line selection ofmultiplexers 606, 608.

[0081] With continued reference to FIG. 7, DSP 600, together withmultiplexers 606, 608, may be provided on encoder 626 within transmitter500. Encoder 626 accepts the four digitized audio inputs 602, 603, 604,605 from audio modules 622, 623, 624, 625 and uses line driver 631 tosend digitized serial data stream 633 to IR transmitter module 634 fortransmission to headphones 80.

[0082] Baseboard 626 also includes clock and clock phasing circuitry628, boot/program memory 630, and power supply 632. DSP 600 serves asthe central control for the encoder 626 circuitry, including control ofall inputs and outputs of audio transmission device 500. A clockingdivider provided within clocking circuit 628 is activated by DSP 600 toprovide signals to drive the clocks for any audio modules (e.g. ADCs)and audio data inputs to the DSP. DSP 600 combines audio data 610, 612from two serial sources (multiplexers 606, 608) and formats the audiodata into single serial data stream 633 of data packets that is providedto line driver 631 to send to IR transmitter 634. In one embodiment,line driver 631 may be a differential line driver with an RS485transceiver, and an inverter may be used to invert and buffer data fromDSP 600. DSP 600 uses the base 10.24 MHz clock of clocking circuit 628multiplied by a phase locked loop (PLL) internal to the DSP. In oneembodiment the DSP clock speed is 8×MHz, but this may be reduced so asto reduce overall power consumption by audio transmission device 500.

[0083] With continued reference to FIG. 7, boot memory 630 stores theprogram memory for DSP 600 (that contains the software controlling theDSP) during shut down. An 8-bit serial EEPROM may be used as boot memory630. Upon power up the DSP may be programmed to search external memorycircuits for its boot program to load and commence executing. Bootmemory 630 is attached to multi-channel buffered serial port 615(McBSP 1) of DSP 600. In alternative embodiments the DSP software may beprovided in DSP read-only-memory (ROM).

[0084] With reference now to FIG. 8, clock and clock phasing circuitry628 develops all clocks required by encoder 626 and audio modules 622,623, 624, 625. Four separate clocks are required for the DSP, audio datatransfer and audio digitizing. These are master clock 660, serial clock661, left/right clock 662 and multiplexer clock 663. Clock phasing isalso required by multiplexers 606, 608 to multiplex digitized audioinput streams 602, 603, 604, 605 as previously described with respect toFIG. 6. Master clock 660 is used to drive the master-synchronizing clocksignal for the audio digitizing modules and the DSP. Master clock signal660 is generated from stand-alone crystal oscillator circuit 660 and hasbuffered output 661. The master clock frequency is 10.24 MHz, whichallows the derivation of the serial clock and left/right clock from themaster clock. The serial clock is used to clock each individual bit ofdigitized audio input streams 602, 603, 604, 605 from audio modules 622,623, 624, 625 into DSP 600. Serial clock signal 661 is derived from themaster clock using one-fourth clock divider 667 to generate a clockingsignal at a frequency of 2.56 MHz.

[0085] The left/right clock is used to clock the Left and Right datawords from digital audio data streams 610, 612 generated by multiplexers606, 608 for input to DSP 600, and to develop the DSP frame sync.Left/right clock signals 662 are derived from the master clock usingclock divider 667 to generate a signal at a frequency that is 256 timesslower than the master clock. Clock phasing circuitry 668 separates theleft/right clock into two phases by providing a 90-degree phase shiftfor one of the left/right clocks. This allows two of the four audiomodules 622, 623, 624, 625 to produce a 90-degree phase shifted output.The outputs of the in phase left/right clocked audio module outputs aremultiplexed with the 90 degrees phase shifted data on one line. Eachleft/right clock phase serves as a separate frame sync for digitizedaudio input streams 602, 603, 604, 605 from audio modules 622, 623, 624,625.

[0086] Multiplexer clock 663 is used by the multiplexer logic fortoggling the selected input data lines to combine the digital audiopackets in digitized audio input streams 602, 603, 604, 605 from audiomodules 622, 623, 624, 625. Multiplexer clock signal 663 is alsogenerated by clock divider 667. DSP clock signal 664 is used to driveDSP 600 and is generated by converting master clock signal 660 to alower voltage (e.g. 1.8V from 3.3V), as required by the DSP, bybuffer/voltage converter 669. Other clocking schemes may be used bychanging the base crystal oscillator frequency (i.e. the 9.216 MHz baseclock for a 40 KHz left/right clock may be changed to a 11.2896 MHz baseclock for a 44.1 KHz left/right clock).

[0087] Power supply 632 develops all of the required voltages forencoder 626. In one embodiment, encoder power supply 632 may accept aninput voltage range from +10 VDC to +18 VDC. Four separate voltages maybe used on the transmitter baseboard; Input voltage (typically +12 VDC),+5 VDC, +3.3 VDC, and +1.8 VDC. Transient protection may be used toprevent any surges or transients on the input power line. A voltagesupervisor may also be used to maintain stability with DSP 600. Theunregulated input voltage is used as the source voltage for the +5 VDC.A regulated +5 VDC is used to supply IR transmitter module 634. Audiomodules 622, 623, 624, 625 use +5 VDC for input audio protection andinput audio level bias. IR transmitter 634 uses +5 VDC for bias controland IR driver circuit 650. Regulated +3.3 VDC is used to supply DSP 600and logic of encoder 626, and is also supplied to the audio modules fortheir ADCs. The +3.3 VDC is developed from the regulated +5 VDC supplyvoltage and is monitored by a voltage supervisor. If the level fallsbelow 10% of the +3.3 VDC supply, the voltage supervisor may hold DSP600 in reset until a time period such as 200 ms has passed after thevoltage has increased above +3.0V. Regulated +1.8 VDC is used to supplythe DSP core of encoder 626 and is developed from the regulated +3.3 VDCsupply voltage.

[0088] Referring now to FIG. 9, in one embodiment audio modules 622,623, 624, 625 may be used to provide digitized audio input streams 602,603, 604, 605 to DSP 600. The audio modules may be external or internalplug-in modules to encoder 626 or may be incorporated into the encoder.In an embodiment providing four channels of audio, four audio modulesmay be used with the transmitter baseboard. Each audio module (e.g.audio module 622 shown in FIG. 9) accepts one stereo audio pair (leftand right) of inputs 638, 639. Power and the master clock, serial clock,and left/right clock are all supplied by encoder 626. Signalconditioning and input protection circuitry may be used to prepare thesignals 638, 639 prior to being digitized and protect the inputcircuitry against transients.

[0089] Signals 638, 639 are conditioned separately. DC Bias circuit 640sets signals 638, 639 to the midrange of the five-volt power supply soas to allow the input signal to be symmetric on a DC bias. In thismanner, any clipping that occurs will occur equally on each positive andnegative peak. Input Surge Protection circuit 641 may be used to protectthe input circuitry against transients and over voltage conditions.Transient protection may be provided by two back-to-back diodes insignal conditioning and input protection circuit 640 to shunt any highvoltages to power and to ground. Line level inputs may be limited to twovolts, or some other practicable value, peak to peak. Low pass filter642 may be provided to serve as a prefilter to increase the stopbandattenuation of the D/A internal filter. In one embodiment, each analoginput audio channel frequency is 20 Hz to 18 KHz and the low pass filter642 corner frequency is above 140 KHz so that it has minimal effect onthe band pass of the audio input.

[0090] With continued reference to FIG. 9, ADC 643 is used to digitizeboth left and right analog inputs 638, 639. Single serial digital datastream 602 containing both the left and right channels is output by ADC643 to encoder 626. The 10.24 MHz master clock is used to develop thetiming for ADC 643, and the 2.56 MHz serial data clock is used to clockthe data from the ADC. The 40 KHz left/right clock is used to frame thedata into distinct audio samples. Each left and right analog sample maybe a 16-bit value.

[0091] With reference now to FIG. 10, IR transmitter or module 634converts digital data stream 633 to an IR (Infrared) transmissionsignals 16. PPM (Pulse Position Modulation) encoding is used to increasetransmitter power by using a bit position value. IR transmitter 634includes line receiver 650 to receive differential RS485 signal 633 fromline driver 631 and transform it into a single ended data stream. Thedata stream is then buffered and transferred to infrared bias andcontrol circuits 650, which drive the light emitting diode(s) (LEDs) ofemitters 652 and control the amount of energy transmitted. In oneembodiment of the invention, IR transmitter 634 includes four infraredbias and control circuits 650 and four respective emitters 652, with a25% duty cycle for each emitter 652. Bias control maintains the IRemitter(s) in a very low power-on state when a zero bit is sensed indata stream 633 to allow the direct diode drive to instantly apply fullpower to the IR emitter diodes when a positive pulse (one bit) issensed. A sensing resistor is used to monitor the amount of currentsupplied to the diodes such that when the emitter diode driver is pulsedthe bias control maintains a constant current flow through the diodes.IR emitters 652 transform digital data stream 633 into pulses ofinfrared energy using any practicable number (e.g. four per IR emitter)of IR emitter diodes. The bandwidth of the electrical data pulses aremainly limited by the fundamental frequency of the square wave pulsesapplied to the IR emitter diodes due to the physical characteristics ofthe diodes. In one embodiment, the IR energy may be focused on a centerwavelength of 870 nM. Encoder 626 supplies all power to IR transmittermodule 634. +5 VDC is used for driver and bias control circuitry 650. Inone embodiment, encoder 626 supplies PPM-encoded digital data stream 633to IR transmitter 634 at 11.52 Mb/s.

[0092] Referring now to FIG. 11, MCBSPs 613, 615 and DMAs 614, 616 areused to independently gather four stereo (eight mono) channels of data.When either of the McBSPs has received a complete 16-bit data word, therespective DMA transfers the data word into one of two holding buffers670, 671 (for DMA1 616) or 672, 673 (for DMA0 614) for a total of fourholding buffers. Each McBSP 613, 615 uses it's own DMA 614, 616 andbuffer pair 672/673, 670/671 to move and store the digitized data. Whileone buffer is being filled DSP 600 is processing the complementarybuffer. Each buffer stores twenty-five left and twenty-five right datasamples from two different ADCs (for a total of 100 16-bit samples).Each word received by each McBSP increments the memory address of therespective DMA. When each buffer is full, an interrupt is sent from therespective DMA to DSP 600. DSP 600 resets the DMA address and the otherbuffer is filled again with a new set of data. This process iscontinuously repeated.

[0093] DSP 600 creates two transmit buffers that are each the size of afull transmit packet 86. In one embodiment, 450 (16-bit) words are usedin each packet (as more fully discussed below). When a packet 86 isfirst initialized, static header/trailer values are inserted in thepacket. For the initial packet and subsequent packets, the UserID/Special Options/Channel Status (USC) values of control block 96, dataoffsets, dynamic header values, and channel audio data are added to eachpacket. The USC values calculated from the previous packet audio dataare preferably used. The audio data is PPM encoded and placed in datablocks packet. Once a predetermined number (e.g. twenty-five) of samplesfrom each channel have been processed, packet 86 is complete.

[0094] When DSP 600 fills one of the output buffers completely, atransmission DMA (DMA2) is enabled. DMA2 then transfers the data in thefilled output buffer to a serial port (McBSP0) of transmission device500. McBSP0 in turn sends serial data 633 to line driver 631 to send toIR transmitter 634. Once the Output DMA and McBSP are started, theyoperate continuously. While DSP 600 fills one of the buffers, the otherbuffer is emptied by DMA2 and sent to McBSP0. Synchronization ismaintained via the input data.

[0095] DSP 600 handles interrupts from DMAs 614, 616, monitors SpecialOptions and Channel Status information as described elsewhere herein,constructs each individual signal (or transmission packet) 86, andcombines and modulates the audio data and packet information. The DMAinterrupts serve to inform DSP 600 that the input audio buffer is full,at which time the DSP reconfigures the respective DMA to begin fillingthe alternate holding buffer and then begins to process the “full”holding buffer. No interrupt is used on the output DMA. Once the outputbuffer is full, the output DMA is started to commence filling the otherbuffer.

[0096] As more fully described elsewhere herein, Special Optionsinformation may be used to indicate if audio transmission device 500 isbeing used in a unique configuration and may be provided throughhardware switches or hard coded in the firmware. Special Options mayinclude, but are not limited to, 5.1 and 7.1 Surround Sound processing.In one embodiment, four bits may be used to indicate the status of theSpecial Options. Four bits will provide for up to four user selectableswitch(es) or up to fifteen hard coded Special Options. The Headphonenormal operation may be a reserved option designated as 0000h.

[0097] When a switch option is used, a minimum of one or more of thefifteen Special Options will be unavailable for additional options (i.e.if two switches are used, only four additional Special Options may beavailable. If four switches are used, no additional Special Options maybe available.) For instance, to utilize a 5.1 or 7.1 Surround Soundoption, a hardware switch may be used to toggle a bit level on a HPI(Host Port Interface) of DSP 600. A one (high) on the HPI may indicatethat an option is used. A zero (low) on the HPI may indicate normalfour-channel operation. DSP 600 may read the HPI port and set theappropriate bit in the Special Options value.

[0098] Channel Status information may be used to indicate which stereochannels (left and right channels) contain active audio data. Theamplitude of the digital audio data may determine whether a stereochannel is active or inactive. If active audio is not detected on astereo channel, the Channel Status can be flagged in the outgoingpackets as OFF (zero). If active audio is sensed on a stereo channel theChannel Status can be flagged in the outgoing packets as ON (one).

[0099] In one embodiment, to determine if a stereo channel is active,the absolute values for each set of the four stereo channel data samplesare accumulated. Twenty-five samples (the number of individual channeldata samples in one packet) of each left channel and each right channelare combined and accumulated. If the sum of the stereo channel samplesexceeds the audio threshold, the Channel Status may be tagged as active.If the total of the stereo channel samples does not exceed the audiothreshold, the Channel Status may be tagged as inactive. Four bits (onefor each stereo channel) may be used to indicate the stereo ChannelStatus and preferably are updated each time a packet is created.

[0100] Referring to FIG. 12, an embodiment according to the inventionfor encoding the four channels into individual signals or transmissionpackets 86 is shown to partition each signal 86 into header section 87and data section 88. Header section 87 contains all of the informationfor receiver 700 (detailed herein below) to sense, synchronize andverify the start of a valid transmission packet 86. In one possibleembodiment, the header section includes Preamble, Terminator, and Gapvalues that are not PPM encoded, and further includes Product Identifierand Data Offset values that are PPM encoded.

[0101] Gap value 90 may be a 32-bit (double word) value used by receiver700 to sense header section 87 and synchronize with transmission packet86. Gap 90 may be composed of a Sense Gap, a Trigger Gap, and a SyncGap. The Gap is preferably not PPM encoded and is a static value that isnever changed. The first part of Gap 90 is the Sense Gap, which containsseven leading zeros. These bits are used by receiver 700 to recognizethe beginning of the Gap period. The second part of Gap 90 is theTrigger Gap, which contains alternating one and zero bits. These bitsare by receiver 700 to stabilize the clock recovery circuitry over theGap period. The third part of the Gap is the Sync Gap, which containsthree zero bits. These bits are used by receiver 700 to mark thebeginning of each transmission packet 86.

[0102] Preamble PRE may consist of a predetermined number of equalvalues (e.g. AAAA hexadecimal) to further enable synchronization ofreceiver 700 with transmitter 500. The preamble consists of two separate16-bit (double word) values 89, 91 and are used by receiver 700 toidentify the start of each packet 86. The Preamble is also used toassist in stabilizing the clock recovery circuitry. The Preamble is notPPM encoded and may be a static value that is never changed. Preambleword 89 is preferably placed at the start of packet 86 and the otherpreamble word 90 preferably follows Gap 90. The Preamble words arecomposed of alternating ones and zeros (AAAAh). The first “one” bit ofthe second Preamble word 91 may signal the start of the particularpacket 86.

[0103] Following the second Preamble word 90 is predetermined code orunique identifier ID (PID) 92, which may be selected to uniquelyidentify transmitter 500 to receiver 700. PID 92 is preferably PPMencoded and is a static value that does not change. This feature may beused, for example, to prepared headphones according to the inventionthat may only be used in a car, or a particular make of car, or with aparticular make of transmitter. Thus, for headphones used in a museumwherein visitors rent the headphones, the receivers in the headphonesmay be programmed to become operation only upon detection of a uniqueidentifier ID that is transmitted only by transmitters 500 installed inthe museum. This feature would discourage a visitor frommisappropriating the headphones because the headphones would simply notbe functional anywhere outside of the museum. This feature may furtherbe used to control quality of after market accessories by an OEM. Forinstance, a vehicle manufacturer or a car audio system manufacturer mayinstall transmitters according to the invention in their equipment butcontrol the licensing/distribution of the unique ID transmitted by theirequipment to those accessory (headphones, loudspeakers, etc.)manufacturers that meet the OEMs particular requirements.

[0104] Following PID 92 is data offset value (DO) 93 followed by offsetportion 94, the final portion of header section 87. Offset value 93indicates the length of (i.e. number of words in) offset portion 94 anddata filler portion 97, and may be a fixed value that is constant andequal in each transmitted signal or packet 86, or alternatively may bedynamically varied, either randomly or according to a predeterminedscheme. Varying the length of the offset portion from signal to signalmay help avoid fixed-frequency transmission and/or reception errors andreduce burst noise effects. Offset portion 94 and data filler portion 97together preferably contain the same number of words (e.g. 30), andthereby allow the random placement of data section within a particularpacket 86 while maintaining a constant overall length for all packets.Offset portion 94 serves to space unique PID 92 from data section 88 andmay contain various data. This data may be unused and thus composed ofall random values, or all zero values, to be discarded or ignored byreceiver 700. Alternatively, offset portion 94 may contain data used forerror detection and/or error correction, such as values indicative ofthe audio data or properties of the audio data contained in data section88.

[0105] Data section 88 is formed by interleaving data blocks 95 withcontrol blocks 96. In one embodiment data block 95 consist of 5 samplesof 4 channels of left and right encoded 16-bit values (1 word) of audioinformation, for a total of 80 PPM-encoded words. Data blocks 95 mayconsist of any other number of words. Furthermore, the data blocks ineach signal 86 transmitted by transmitter 500 do not have to containequal numbers of words but rather may each contain a number of wordsthat varies from signal to signal, either randomly or according to apredetermined scheme. Consecutive data blocks 95 within a single packet86 may also vary in length. Additionally, consecutive packets 86 maycontain varying numbers of data blocks 95 in their data sections 88.Indicators representing, e.g., the number of data blocks and the numberof words contained in each data block may be included in header block 87of each packet 86, such as in offset portion 94, to enable transmitter700 to properly process the data contained in each packet 86.

[0106] Control block 96 follows each data block 95, and in oneembodiment includes the Special Options and Channel Status informationdiscussed previously, as well as a predetermined code or uniqueidentifier User ID. As described elsewhere herein, User ID may be avalue used for error detection, such as by comparing a User ID valuecontained in header 87 with each successive User ID value encountered insubsequent control blocks 96. If the values of User ID throughout apacket 86 are not identical, the packet may be discarded as a bad packetand the audio output of the headphones may be disabled after apredetermined number of sequential bad packets has been received. TheUser ID may further be used to differentiate between varioustransmission devices 500 such that, for instance, a receiver 700programmed for use with a transmission device installed in a particularmanufacturer's automobile will not be useable with the transmissiondevices in any other manufacturers automobiles or in a building such asa museum or a private home (as further detailed elsewhere herein).Channel Status information may be used to control the channel selectionswitch on receiver 700 to only allow selection of an active channel, andto minimize power consumption by powering down the receiver DSP to avoidprocessing data words in each packet 86 that are associated with aninactive channel, as more fully described elsewhere in thespecification.

[0107] At the end of data section 87 is end block or terminator block(TRM) 98. TRM 98 is preferably a 16-bit (single word) value and may beused by receiver 700 to allow a brief amount of time to reconfigure theMcBSP parameters and prepare for a new packet 86. TRM 98 may also beused to assist in stabilizing the receiver 700 hardware clock recoveryover the GAP 90 period, and may also contain data for error detectionand/or correction, as discussed elsewhere. TRM 98 is preferably not PPMencoded and is a static value preferably composed of alternating onesand zeros (AAAAh).

[0108] With reference now to FIG. 13, receiver apparatus or headset unit700 has two separate sections to enable omni-directivity of receptionand to more evenly distribute the circuitry of the receiver throughoutthe enclosure of headphones 80. The main section of the receiver isprimary receiver 702. The secondary module is secondary receiver 704.Both primary receiver 702 and secondary receiver 704 contain an IRreceiver preamplifier. In one embodiment, primary receiver 702 maycontain the bulk of the receiver circuitry and secondary receiver 702may be used as a supplementary preamplifier for IR signal 16 when theprimary receiver IR receiver is not within line of sight of thetransmitted IR signal due to the orientation or location of the listenerwearing headphones 80.

[0109] Referring to FIG. 14, primary receiver 702 contains receiver DSP710, IR receiver/AGC 714, data clock recovery circuit 716, D/A converter(DAC) and audio amplifier circuit 722, user selectable switches andindicators control circuit 718, boot/program memory 730, and powersupply and voltage supervisor circuit 740. DSP 710 serves as the centralcontrol for the receiver 700 circuitry and controls all of the inputsand outputs of the receiver. The IR data packet is received by DSP 710in single serial stream 712 from IR receiver 714. The start of IR datastream 712 creates the frame synchronization for the incoming datapacket. Clock recovery circuit 716 develops the IR data clock used tosample the IR data. The DSP serial port completes clocking for the16-bit DAC. The master clock for the 16-bit D/A converter is developedfrom an additional serial port.

[0110] External switches and indicators 719 may include switches toallow the listener to access functions such as select the desiredchannel and adjust the audio volume. LED indicators may be provided tobe driven by DSP 710 to indicate whether power is supplied to thereceiver and the selected channel. Control circuit 718 interfacesexternal switches and indicators 719 with DSP 710, providing input fromthe switches to the DSP and controlling the indicators as dictated bythe DSP.

[0111] The base clocking for DSP 710 is developed from clock recoverycircuit 716. The input clock to DSP 710 is multiplied by a PLL internalto the DSP. The DSP clock speed is 8×MHz, and may be reduced to minimizeoverall power consumption by receiver 700. DSP 710 can also disable theswitching power supply on secondary receiver 704 via a transistor and aflip-flop. If the software does not detect a valid signal in a setamount of time, the DSP can disable the switching power supply andremove power from the receiver, as detailed elsewhere herein.

[0112] Referring now to FIG. 15, IR Receiver/AGC 714 is used totransform and amplify the infrared data contained in received signal 16.IR Receiver/AGC 714 also controls the amplification and develops digitaldata stream 712 for DSP 710 and data clock recovery circuit 716. Theusable distance for the IR receiver is dependent on variables such astransmitter 500 power and ambient lighting conditions. In oneembodiment, the overall gain of IR Receiver/AGC 714 may be approximately70 dB.

[0113] With continued reference to FIG. 15, IR receiver/AGC circuit 714contains preamplifier 770, final amplifier 771, data squaring stage (ordata slicer) 772, and AGC (Automatic Gain Control) circuit 773. IRpreamplifier 770 transforms optical signal 16 into an electrical signaland provides the first stage of amplification. The IR preamplifier iscomposed of three separate amplifiers. The first amplifier is composedof four IR photo detector diodes and a transimpedance amplifier. In oneembodiment, combined wide viewing angle photo diodes may produce betterthan 120 degrees of horizontal axis reception and 180 degrees ofvertical axis reception. A daylight filter may be incorporated into thephoto detector diode that, together with inductive transimpedanceamplifier feed back, minimizes the DC bias effect of ambient lighting.When IR signal 16 is transmitted, a current pulse proportional to thestrength of the IR signal is generated in the photo detector diodes. Thestrength of the received IR signal is dependent on the distance from thetransmitted IR source.

[0114] The current pulse from the photo diodes is applied directly tothe transimpedance amplifier. The transimpedance amplifier senses therising and falling edges of the current pulse from the photo detectordiodes and converts each pulse into a voltage “cycle.” The secondamplifier is a basic voltage amplifier. The output of the second stageis controlled by AGC circuit 773. The third amplifier is also a basicvoltage amplifier. The output of the third stage of preamplifier 770 isfed the input of final amplifier stage 771 and AGC 773.

[0115] Final amplifier stage 771 is used to further increase the gain ofreceived IR signal 16 and also serves as a combiner for Headphone—Leftand Headphone—Right preamplifiers 750, 770. Final amplifier 771 iscomposed of two basic voltage amplifiers. Each of the two stages ofamplification increases the gain of the received IR signal. The inputsignal to the final amplifier is also controlled by the second stage ofAGC 773, as described below. The output of the final amplifier stage isfed to AGC 773 and data squaring stage 772.

[0116] AGC 773 controls the amplified IR signal level. The AGC circuitryis composed of one amplifier and three separate control transistors. Thethree separate control transistors comprise two levels of AGC control.The first level of AGC control uses two AGC control transistors (one foreach stage) and is performed after the first voltage amplifier in boththe Headphone—Left and Headphone—Right preamplifier stages 750, 770. Thesecond level of AGC control occurs at the junction of both ofpreamplifier 750, 770 output stages and the input to final amplifierstage 771. To develop the AGC DC bias voltage, the positive peaks of theIR signal from the final amplifier stage output are rectified andfiltered. The DC signal is amplified by an operational amplifier. Thevalue of the amplified DC voltage is dependent on the received signalstrength (i.e. proportional to the distance from IR emitters 652 oftransmission device 500). The AGC transistor resistance is controlled bythe DC bias and is dependent on the received signal strength. When thesignal strength increases, the bias on the AGC transistors increases andthe signal is further attenuated. AGC 773 thus produces a stable analogsignal for data squaring stage 772.

[0117] Data squaring stage 772 produces a digitized bi-level—square wave(i.e. composed of ones and zeros) from the analog IR signal. The inputfrom the data squaring stage is received from the output of finalamplifier stage 771. The data squaring stage compares the finalamplifier 771 output voltage “cycle” to a positive and negativethreshold level. When the positive peak of the final amplifier outputexceeds the positive threshold level, a high pulse (one bit) isdeveloped. When the negative peak exceeds the negative threshold level,a low pulse (zero bit) is developed. Hysteresis is accounted for toprevent noise from erratically changing the output levels. The output ofdata squaring stage 772 is sent to clock recovery circuit 716 and as IRdata input 720 to DSP 710.

[0118] Data clock recovery circuit 716 is used to reproduce the dataclock used by transmitter 500. In one embodiment of receiver 700 of theinvention, the data clock recovery circuit contains an edge detector anda PLL (Phase Lock Loop). The data clock recovery circuit 716 utilizesthe PLL to generate and synchronize the data clock with the incoming IRdata 720. The edge detector is used to produce a pulse with each risingor falling bit edge so as to create a double pulse for additional datasamples for the PLL. A short pulse is output from the edge detector whena rising or falling pulse edge is sensed. The output from the edgedetector is fed to the PLL.

[0119] The PLL is used to generate a synchronized clock, which is usedby DSP 710 to sample the IR data signal 712. A frequency and phasecharge pump comparator circuit in the PLL compares the edge detectorsignal to a VCO (Voltage Controlled Oscillator) clock output from thePLL. The output of the comparator is sent to a low pass filter. The lowpass filter also incorporates pulse storage. The pulse storage isrequired since the data is PPM (Pulse Position Modulated) and does notprovide a constant input to the PLL comparator. The low pass filterproduces a DC voltage used by the VCO of the PLL. The VCO produces anoutput frequency proportional to the DC voltage generated by the lowpass filter. When the voltage from the loop filter rises the VCOfrequency also rises, and visa versa. When the clock output of the VCOis synchronized with edge detector output, the low pass filter voltageand VCO frequency stabilize. The VCO frequency remains locked in syncwith the edge detector until a phase or frequency difference developsbetween the VCO frequency and the edge detector signal. The output ofthe VCO is used as the data sample clock for serial port 711 of DSP 710and it is also used as the base clock frequency of the DSP. Receiver DSP710 uses the recovered data clock to synchronize with transmitter DSP600 such that the data encoded and transmitted by transmitter 500 isreceived and decoded by receiver 500 at the same rate. The PLL alsocontains a lock detect, which can be used to signal DSP 710 when the PLLis locked (synchronized with the incoming data). Thus, by the method ofthe invention, the incoming data clock is recovered continuously byreceiver 500 as the incoming data packets are processed, not just whenthe header of each data packet is processed.

[0120] With reference to FIG. 16, in an alternative embodiment ofreceiver 700 of the invention includes data clock recovery circuit 716that does not utilize a PLL but rather employs edge detector 775,crystal oscillator 776 tuned to the frequency of the audio transmissiondevice 500 master clock, and buffers 777, 778 to synchronize the dataclock with incoming IR data 712. Edge detector 775 is used to produce apulse with each rising bit edge. A combination of four NOR gates areused to create a short pulse that is output by the edge detector when arising edge is sensed. This provides a synchronizing edge for crystaloscillator 776. The first NOR gate of the edge detector provides a trueinversion to the data stream. The output from the first NOR gate is sentto a serial port of DSP 710. The second NOR gate provides abuffer/delay. The output from the second NOR gate is fed to a RC timeconstant (delay). The third NOR gate triggers from the RC time constant(delay). The fourth NOR gate collects the outputs of the first and thirdgates. This provides a short sync pulse for crystal oscillator 776.

[0121] Crystal oscillator 776 and buffer stages 777, 778 provide abi-level clock for sampling the IR data 712. The crystal oscillatorutilizes a crystal frequency matched to the outgoing transmission device500 data clock frequency. A parallel crystal with an inverter is used toprovide a free running oscillator. The pulse developed from the edgedetector provides synchronization with received data stream 712. Twoinverter/buffers 777, 778 are used to provide isolation for crystaloscillator 776. The buffered output is sent to the DSP serial port dataclock input and voltage conversion buffers. The voltage conversionbuffers decrease the clock peak level to 1.8 volts for the DSP coreclock input.

[0122] With reference now to FIG. 17, DAC and audio amplifier circuit722 develops analog signal 724 from digitized data stream 721 output byDSP 710, and further amplifies and buffers the output to headphonespeakers 81, 83. DAC and audio amplifier circuit 722 includes DAC 780,which may be a 16-bit DAC, for receiving serial digital audio datastream 721 from DSP serial port 713 (from the channel selected by DSP710 in accordance with listener selection via switches 719) to produceseparate left and right analog signals 724 from digital serial datastream 721. The digital data stream 721 is converted essentially in areverse order from the analog-to-digital conversion process in audiomodules 622, 623, 624, 625. The output of DAC 780 is sent through lowpass filter 781 (to remove any high frequencies developed by the DAC) toaudio amplifier 782. Audio amplifier 782 amplifies the audio signal andprovides a buffer between the headphones 80 and DAC 780. The output fromaudio amplifier 782 is coupled into headphone speakers 81, 83.

[0123] User selectable switches 718 allow a listener to adjust the audiovolume in headphone speakers 81, 83 and change the audio channel. LEDs(Light Emitting Diodes) may be used to indicate the selected channel.Two manually operated selector switches may be used to adjust thevolume. One press of an up volume button sends a low pulse to DSP 710upon which the DSP increases the digital audio data volume by one levelhaving a predetermined value. One press of a down volume button sends alow pulse to the DSP and the DSP decreases the digital audio data volumeby one level. Other types of switches may also be used, and are notmaterial to the invention. A preselected number, such as eight, of totalvolume levels may be provided by the DSP. All buttons may use an RC(resistor/capacitor) time constant for switch debouncing.

[0124] A manually operated selector switch may be used by the listenerto select the desired audio channel. One press of the channel selectorbutton sends a low pulse to DSP 710 and the DSP increases the channeldata referred to the audio output (via DSP serial port 713). Apredetermined number (e.g. four) of different channels are selectable.When the highest channel is reached the DSP rolls over to the lowestchannel (e.g. channel four rolls into channel one). Alternatively, if achannel is not available, the DSP may be programmed to automaticallyskip over the unavailable channel to the next available channel suchthat the listener never encounters any ‘dead’ channels but rather alwaysselects among active channels, i.e. channels presently streaming audio.A plurality of LEDs (e.g. a number equal to the number of availablechannels, such as four) may be used to indicate the selected channel.The illumination of one of the LEDs may also indicate that power issupplied to the circuitry and that DSP 710 is functioning.Alternatively, an LCD or other type of display may indicate the channelselected, volume level, and any other information. Such information maybe encoded in the header of each data packet, and may include additionaldata regarding the selected audio stream (e.g. artist, song name, albumname, encoding rate, etc.) as well as any other type of information suchas content being streamed on the other available channels,identification of the available (versus unavailable or ‘dead’ channels),environmental variables (speed, temperature, time, date), and messages(e.g. advertising messages). The information displayed may include textand graphics, and may be static or animated.

[0125] Referring once again to FIG. 14, boot memory 730 stores theprogram memory for DSP 710 during shut down. An 8-bit serial EEPROMconnected to serial port 715 of DSP 710 may be used to store the DSPprogram. Upon power-up the DSP may be configured to search for externalmemory to retrieve and load its operating software. Alternatively, theprogram may be provided in DSP read-only-memory (ROM).

[0126] With continued reference to FIG. 14 and also referring to FIG.18, power supply 740 on the primary receiver 702 circuit board receivesDC power 761 from switching power supply 760 in secondary receiver 704.Power supply 640 receives DC power from supply 759 (e.g. AAA batteriesor any other type or size of batteries, or alternatively DC via a powercord from a vehicle or building power system, or any other practicablepower supply) and includes a +1.8V (or other voltage, as required by theDSP circuitry) supply and associated voltage supervisor. The regulated+1.8 VDC is used to supply the DSP core of DSP 710 and is developed froma regulated +3.3 VDC supply voltage. A voltage supervisor is used tomonitor the +3.3 VDC. If the level drops below 10% of the +3.3 VDCsupply, the voltage supervisor may hold the DSP in reset. If the levelfalls below 10% of the +3.3 VDC supply, the voltage supervisor may holdDSP 710 in reset until a time period such as 200 ms has passed after thevoltage has increased above +3.0V.

[0127] With continued reference to FIG. 18, secondary receiver 704supplies power 761 to receiver system 700 and works as a supplementarypreamplifier for IR signal 701 when primary receiver IR receiver 714 isnot within a direct line of sight of transmitted IR signal 16. Secondaryreceiver 704 includes IR receiver preamplifier 750, switching powersupply 760, and on/off switch 762. IR receiver preamplifier 750amplifies IR analog signal 16 when line-of-sight is not available toprimary receiver IR receiver 714. The two stages of the secondaryreceiver IR receiver preamplifier are the same as in primary receiver702, and the output of the second stage is provided to the input of AGC773 in IR receiver and AGC circuit 714 of primary receiver 702.

[0128] Switching power supply 760 converts battery 759 voltage to thelevel used by the receiver 700 circuitry. The majority of secondaryreceiver and primary receiver circuitry operates on 3.3 VDC (@<200 mA).The switching supply generates 3.3 VDC from two AAA batteries 759.Switching power supply 760 is able to source power from batteries 759down to 0.9 volts utilizing a charge pump (inductor-less), oralternatively a boost-type, converter. A low pass filter may be used toremove the high frequency components of switching power supply 760.

[0129] On/off switch 762 enables and disables switching power supply760. The on/off switch circuit 762 is powered directly by batteries 759.Inputs 718 to on/off switch circuit 762 include a manually operatedswitch and DSP 710. A manually operated SPST (Single Pole Single Throw)switch is connected to the clock input of a flip-flop, wherein eachpress of the SPST switch toggles the flip-flop. A RC(resistor/capacitor) time constant is used to reduce the ringing andtransients from the SPST switch. A high output from the flip-flopenables switching power supply 760. A low output from the flip-flopdisables switching power supply 760 and effectively removes power fromthe receiver 700 circuit. DSP 710 can also control the action of theflip-flop. If the software does not detect a valid signal in a setamount of time, DSP 710 may drive a transistor to toggle the flip-flopin a manner similar to the manually operated SPST switch.

[0130] With reference once again to FIG. 14, in operation DSP 710activates an internal DMA buffer to move the PPM4-encoded data receivedon the serial port (McBSP) 711 to one of two received data buffers. Onceall 25 samples of a data packet have been collected, a flag is set totrigger data processing. When the receive buffer “filled” flag is set,data processing begins. This includes PPM4-decoding the selected channelof data, combining the high and low bytes into a 16-bit word,attenuating the volume based on listener selection, and placing thedecoded left and right digitized values for all 25 samples into anoutput buffer DacBuffer. A flag is set when the output buffer is filled,and a second DMA continually loops through the output buffer to move thecurrent data to serial port (McBSP) 713 for transmission to DAC circuit722.

[0131] The receiver of serial port 711 is used for capturing the IRdata. The receiver clock (CLKR) and frame synchronization (FSR) are fromexternal sources. The receiver is configured as single-phase, 1-word,8-bit frame, 0-bit delay, and data MSB first. Received frame-sync pulsesafter the first received pulse are ignored. Received data is sampled ona falling edge of the receiver clock.

[0132] The transmitter of serial port 713 is used to present data to DACcircuit 722 for audio output to headphone speakers 81, 83. Thetransmitter clock (CLKX) and frame synchronization (FSX) are generatedinternally on a continuous basis, as previously described. Thetransmitter is configured as single-phase, 4-word, 16-bit frame, 0-bitdelay, and data MSB first. Transmit data is sampled on a rising edge ofthe transmitter clock.

[0133] The sample-rate generator of serial port 711 is used with DACcircuit 722 and the transmitter of serial port 713. The sample rategenerator uses divide-by-9 of the DSP 710 clock to achieve a frequencyof 8.192 MHz. The transmit frame-sync signal is driven by the samplerate generator with a frame period of 64 clock cycles, and a frame widthof 32. The sample-rate generator of serial port 711 is the master clock.The sample rate generator uses divide-by-4 of the DSP 710 clock. Thetransmit frame-sync signal is driven by the sample rate generator with aframe period of 16 clock cycles.

[0134] The DMA buffers of receiver 700 are configured generallysimilarly to those of transmitter 500. The DMA priority and controlregister also contains the two-bit INT0SEL register used to determinethe multiplexed interrupt selection, which should be set to 10 b toenable interrupts for DMA 0 and 1. DMA 0 is used to transfer IR data 712received using the receiver of serial port 711 to one of two buffers.The source is a serial port 711 receive register DRR1_(—)0. Thedestination switches between one of two received data buffers, RxBuffer1and RxBuffer2. The counter is set to the size of each buffer, which maybe 408 words. The sync event is REVT0 in double word mode for 32-bittransfers. The transfer mode control is set for multi-frame mode,interrupt at completion of block transfer, and post-increment thedestination. DMA 2 is used to transfer the single channel of digitalaudio to DAC circuit 722. The source is the DSP output buffer DacBuffer.The destination is a serial port 713 transmit register DXR1_(—)0. Thecounter is set to the size of the DacBuffer, which may be 4 words. Thesync event is XEVT0. The transfer mode control is set for autobuffermode, interrupts generated at half and full buffer, and post-incrementthe source.

[0135] The serial port 711 receiver ISR is used to check whether datastream 712 in synchronized. A received data state machine begins indwell mode where the received data is examined to determine whensynchronization is achieved. Normal operation begins only aftersynchronization. The serial port 711 receiver ISR first checks forpreamble PRE in data stream header block 90. When this synchronizationis detected, the receiver of serial port 711 is set to a dual-phaseframe: the first phase is 128 32-bit words per frame with no frameignore, the second phase is 73 32-bit words per frame with no frameignore. This combinations produces the equivalent of 402 16-bit words.The state machine proceeds to check that subsequently received wordsform a predetermined code. When this synchronization is detected, DMA 0is initialized with its counter length set to half the size of thereceive buffer, RxBuffer, which is 408/2 =204 words. The destination isthen set to the current receive buffer, RxBuffer1 or RxBuffer2. Next DMA0 is enabled and the serial port 711 receiver ISR is turned off. Thestate machine is placed in dwell mode in advance of the next loss ofsynchronization. If the data stream goes out of sync, the serial port711 receiver is set to a single-phase, 4-word, 8-bit frame with no frameignore, and the serial port 711 receiver ISR is turned on.

[0136] If the predetermined code is not detected, a reception error maybe presumed to have occurred and a counter within DSP 710 may beinitialized to count the number of packets received wherein the encodedvalue is not detected. After a preselected number of such occurrencesare counted the DSP may mute the audio output to the headphones. Mutingbased on detection of a preselected number of such occurrenceseliminates buzzing and popping sounds, and intermittent sound cut-offthat can occur when repeated reception errors are encountered. The DSPmay be programmed to mute the audio output after the first error isencountered, or after a larger number of errors (e.g. 10, 50, 100, etc.)have been counted. Upon muting the audio output to the headphones, theDSP waits for the next packet where the code is detected and then eitherprovides the audio output the headphones once again or waits until apredetermined number of data packets with no errors have been received,at which time it may be presumed that the reasons that led to theprevious reception errors are no longer present and the system is onceagain capable of clear reception. If a packet with no errors is notreceived for a certain time (e.g. 60 seconds) the DSP may initiate theauto-off feature and power off receiver 700, at which time the listenerwould have to activate manual switch 762 to turn the system back onagain. Additionally, the auto-mute or auto-off features may be engagedif a predetermined amount of time passes and no headers are processed atall, due to the audio device 34 being turned off or to noise (e.g.bright light interfering with photoreception).

[0137] When DMA 0 completes its transfer, the synchronization procedureis restarted. DMA 0 is turned off, the serial port 711 receiver isturned on, and the current buffer index is toggled to indicate RxBuffer1or RxBuffer2. A flag is next set indicating that the DMA transfer iscomplete. A main loop in DSP 710 waits for a flag to be set (in DMA 0ISR) indicating that a packet containing the 4 channels of audio hasbeen received and transferred to one of two receive buffers. When thisflag is set, output processing by DSP 710 commences. Output processingconsists of determining the current buffer based on the buffer index,then using the selected channel data to retrieve and decode thePPM4-encoded left and right channel data. The selected volume level isapplied to attenuate the digital signal, and then the final digitalsignal for the left and right earphones is placed in a current outgoingdata block for transmission to DAC circuit for conversion andamplification as described previously with reference to FIG. 14.

[0138] The embodiments described previously are only examples ofwireless communication systems according to the invention, and numerousmodifications and additions may be made to these embodiments in keepingwith the novel concepts the invention. These include hardware andsoftware modifications, additional features and functions, and uses forthe communication method of the invention other than, or in addition to,audio streaming.

[0139] Thus, with reference now to FIG. 19, in a further embodiment ofthe present invention vehicle 800 may be provided with communicationsystem 801 according to the invention. Vehicle 800 is shown to be anautomobile, but may be any other type of vehicle such as a bus, a traincar, a naval vessel, or an airplane. Vehicle 800 will typically includefactory-installed audio device 34, which may be a typical in-dash headunit comprising a radio tuner, a cd player or a cassette tape player,and an amplifier. Audio device 34 is shown powered by power system 802(e.g. battery, alternator, etc.) of vehicle 800.

[0140] System 801 includes plug-in unit 820 that contains transmittersubsystem 12 and IR transmitter driver 22, and is connected to audiodevice 34 to receive at least one channel of stereophonic audio datatherefrom. Other sources of data, e.g. a video device such as DVD player832 and an audio device such as MP3 player 834, may be connected toplug-in unit 820. The plug-in unit may accept digital and analog data,as previously described, and is preferably powered by audio device 34.Communication system further includes transmitter 806 containing IRlight emitting diode (LED) 20, and wiring harness 804 to connect plug-inunit 820 with transmitter 806. Alternatively the entire IR transmittersection 18, including IR transmitter or LED 20 and IR transmitter driver22, may be contained within transmitter 806.

[0141] As previously described, transmitter subsystem 12 receivesmultiple channels of audio data and generates a single digitized audiosignal. The digitized audio signal is provided to IR transmitter driver22 which generates an appropriate electric current to operate LED 20 toemit IR signals 16. If IR transmitter driver 22 is contained withinplug-in unit 820, then this electric current is carried by wiringharness 804 to LED 20 in transmitter 806. Alternatively, if IRtransmitter driver 22 is contained within transmitter 806, then thedigitized audio signal generated by transmitter subsystem 12 is carriedby wiring harness 804 to the IR transmitter driver.

[0142] This segmented design, comprising three discrete components(plug-in unit 820, wiring harness 804, and transmitter 806) offers easeof installation of system 801 in vehicle 800 as an after-market additionafter the vehicle has left the factory. The plug-in unit is installed inthe dashboard of the vehicle and requires a single connection to thein-dash head unit or audio device 34, and optionally a connection toeach additional audio source. Alternatively, audio device 34 may becapable of providing multiple concurrent channels of audio to plug-inunit 820, in which configuration a single connection to audio device 34is required.

[0143] Transmitter 806 must be installed at a location that will providea sufficiently broad direct line-of-sight to the rear of the vehicle. Ina preferred embodiment, the transmitter is installed within a dome lightenclosure of vehicle 800. Such installation is further facilitated byincorporating IR transmitter driver 22 within plug-in unit 820, therebyrendering transmitter 806 relatively small because it contains nothingmore than LED 20. Wiring harness is also relatively small because itonly needs to contain a small number of wires to carry a digitizedsignal to either be amplified by IR transmitter driver 22 or to directlyoperate LED 20. In either case, the electric current carried by wiringharness 804 is very low voltage and wattage, and wiring harness ispreferably formed with a small cross-section that further simplifiesinstallation in vehicle 800 because it can easily follow tortuous pathsand requires limited space.

[0144] With continued reference to FIG. 19, system 801 further comprisesdevices equipped to receive signals 16, such as headset unit 14 andloudspeaker 842. The headset units and loudspeaker are both equippedwith an IR receiver 70, respectively, to receive IR signals 16 fromtransmitter 806. The headset units are described in detail elsewhereherein. Loudspeaker 842 is equipped with similar circuitry including IRreceived signal processor 72, decoder 74 with clock, de-multiplexer andcontroller, DSP 76 for digital to analog conversion, as well as one ormore amplifiers to amplify the selected channel.

[0145] In an alternative embodiment, loudspeaker 842 may not include achannel switching selector 78 but rather may be preprogrammed to alwaysplay a preselected channel, e.g., the channel selected at the head unit.In addition, due to higher power requirements, loudspeaker 842 ispreferably powered via a cable by the vehicle power system 802 (notshown in FIG. 16). Alternatively, loudspeaker 842 may be preprogrammedto automatically cut-in and play an emergency channel such as a babymonitor or cell phone channel as previously described.

[0146] Referring to FIG. 20, in a further embodiment of the inventionvehicle 800 may be provided with communication system 801 according tothe invention, as detailed above. As previously described, system 801may include audio device 34, shown powered by power system 802 (e.g.battery, alternator, etc.) of vehicle 800. Audio device 34 may behardwired via wire(s) 804 to transmitter/receiver 806 including an IRtransmitter (e.g. a light emitting diode (LED)) and an IR receiver(photoreceptor). As previously described, audio device 34 can provide aplurality of channels of audio data. In other embodiments, audio device34 can provide other types of data, including video data, cellulartelephone voice data, and text data. Thus, a video device such as DVDplayer 803 may be connected to audio device 34, which in turn can encodethe video signal from the DVD player as discussed previously and provideit to IR transmitter/receiver 806 for transmission toward the rear ofvehicle 800 via IR signals 16. Vehicle 800 may also include cellulartelephone or other wireless communication device 805 that may beconnected to audio device 34, which again can encode a voice stream fromthe telephone for IR transmission. As described below, equipment may beprovided for two-way communication by passengers to converse on thetelephone via audio device 34 and other IR devices according to theinvention.

[0147] System 801 may further include IR repeater 810 that, similar totransmitter/receiver 806, includes an IR transmitter and an IR receiver.Repeater 810 receives IR signals 16 and re-transmits them, increasingthe effective transmission area of system 801. Repeater 810 may bedesigned to relay signals 16 coming from the front of vehicle 800, fromthe rear, or from any other or all directions. Thus, depending upon theapplication, repeater 810 may incorporate multiple receivers facingmultiple directions of reception and multiple transmitters facingmultiple directions of transmission. Repeater 810 requires a powersource (not shown) that may include a battery, a hardwire to the vehiclepower supply, a solar panel installed on the roof of vehicle 800, or anyother practicable or convenient power supply.

[0148] System 801 may optionally include communication subsystem 820including adapter module 822 powered via wire(s) 823 connected to thepower supply of vehicle 800, such as through brake light 824.Transmitter/receiver 826 is connected via wire(s) 827 to module 822 toreceive IR signals 16 and relay to the module, and to receive signalsfrom module 222 to transmit via IR toward other areas of vehicle 800.Module 822 includes circuitry (including a DSP) similar to audio device34 to accept data input and encode the data as described previously forIR transmission by transmitter/receiver 826. The input data may bedigital or analog, and thus module 822 may include one or more ADCs toaccept analog data and digitize it for encoding according to theinvention. Subsystem 820 may be preinstalled by the manufacturer ofvehicle 800, thus allowing a subsequent purchaser of the vehicle toinstall custom IR devices as described below on an as-needed oras-required basis without the need of laborious, complicated additionalwiring installation within the vehicle.

[0149] Module 822 may receive a wide variety of data, including analogor digital video data from video camera 830 for relay to audio device 34via transmitter/receivers 826, 806, and optionally 810. Audio device mayinclude or be connected to video display 831 for displaying the videodata received from video camera 830. Video camera 830 may be mounted atthe rear of the vehicle to provide a real-time display of automobilesbehind vehicle 800 and acting essentially as a rear-view mirror and/or aproximity sensor to alert the driver if another vehicle or otherobstacle is too close to vehicle 800. Module 822 may also accept audioinput from an audio device such as microphone 832. Microphone 832 may beemployed as an audio monitor, e.g. a baby monitor as describedpreviously, or a medical monitor for an ill person travelling in therear of vehicle 800. Microphone 835 may also be used by a person wearingheadphones 80 to access a cellular telephone device (or CB radio, or anyother type of wireless communication device) connected to audio device34, as previously discussed, to receive and conduct a conversationthrough the cellular telephone or other communication device. Thus,microphone 832 may be physically separate from, or alternativelyincorporated into, headphones 80. Headphones 80, or microphone 835, mayincorporate certain controls to access features of the cellulartelephone or other communication device, such as hang-up, dial, volumecontrol, and communication channel selection.

[0150] Module 822 may accept other data input, such as patientmonitoring data (e.g. heartbeat, temperature, etc.) from monitor 833that may be physically applied on a person travelling in vehicle 800 whomay be in need of constant monitoring. Monitor 833 may be any other typeof monitor, and thus may be a temperature monitor for a container to beused to report the temperature of the container to the driver of vehicle800, such as (for example) a food container being delivered by a fooddelivery service.

[0151] System 801 may further include video display device 838 mounted,for example, in the back of a passenger seat for viewing by a passengerseated in a rearward seat (passengers are not shown in FIG. 20 forclarity). Display 838 includes IR receiver 839 for receiving IR signals16 containing, for instance, video data from DVD player 803, or fromvideo camera 830.

[0152] Optionally, game control device 836 may also be connected tomodule 822 for communicating with video gaming console 837 connected toaudio device 34. In this embodiment, passengers may wear headphones 80to listen to the soundtrack of a game software executed by video gamingconsole 837 to generate audio and video signals for transmission byaudio device 34. The video signals may be displayed to the passengers ondisplay device 838, and the passengers may interact with the gamesoftware being executed on the gaming console via inputs through gamecontrol device (e.g. a joystick, touch pad, mouse, etc.) 836.

[0153] Module 822 may further output audio data to audio speaker 840,thereby eliminating the need to extend wires from the front to the rearof vehicle 800 for the speaker. Speaker 840 may be powered by thevehicle power supply, in which case it may include an amplifier toamplify the audio signal received from module 822. Alternatively, module822 may include all circuitry (including a DAC) necessary for processingreceived signals 16 into an analog audio signal and amplifying theanalog signal prior to providing it to speaker 840. The channel playedthrough speaker 840 may be selected through audio device 34 (i.e. by thedriver of vehicle 800) or any other input device including game controldevice 836 (i.e. by a passenger in the vehicle), and the channel thusselected may be indicated in the header of each packet transmitted fromthe audio device for decoding by a DSP within module 822.

[0154] In other embodiments of the encoding schemes previously described(such as the scheme described in connection with FIG. 12), the data maybe arranged in the transmit buffer(s) in various other configurations toreduce processing power consumption by the receiver. As one example, alldata representing one channel may be stored in the buffer (andsubsequently transmitted) sequentially, followed by the next channel andso forth. If a channel or channels are not available, those channels maybe identified in the header of each packet. In this manner, the receiverDSP may power down during the time the inactive channel data is beingreceived.

[0155] When one or more channels are inactive, the transmitter mayincrease the bandwidth allocated to each channel, e.g. by sampling theincoming audio data at a higher rate to provide a higher-quality digitalstream. Alternatively, the transmitter may take advantage of excesscapacity by increasing error detection and/or correction features, suchas including redundant samples or advanced error correction informationsuch as Reed-Salomon values.

[0156] To minimize reception errors, the number of audio samplesincluded in each packet may also be adjusted depending on the number andtype of errors experienced by the receiver. This feature would likelyrequire some feedback from the receiver on the errors experienced, basedupon which the transmitter DSP may be programmed to include fewer audiosamples per packet.

[0157] Other error detection schemes may also be employed with theinvention. As one example, a code may be randomly changed from packet topacket, and inserted not only in the header but also at a location orlocations within the data block. Alternatively, the same encoded valuemay be used. The location(s) of the value(s) may also be randomlychanged from packet to packet to remove the effects of fixed frequencyerrors. The location(s) may be specified in the header of each packet,and the DSP programmed to read the value then check for the same valueat the specified location(s) within the data block. If the value(s) atthese location(s) do not match the value specified in the header, theDSP may discard the packet as containing errors and optionally mute theoutput as described previously.

[0158] To conserve bandwidth and enhance processing efficiency, theencoded value(s) may contain additional information, i.e. instead of arandom value the encoded value may be representative of, for example,the active and inactive channels. The encoded value would preferably beplaced at least in one location of the data block assigned to eachactive channel to ensure that the value is in the channel selected bythe listener for processing by the DSP. In another embodiment, multipleencoded values may be used, each representative of a different systemvariable or other information (e.g. one encoded value indicative ofactive channels, another containing a check-sum value, anothercontaining a Reed-Salomon value for forward error-correction, etc.).

[0159] In a bi-directional system such as system 801, headphones 80 mayinclude an IR transmitter to enable the receiver DSP to transmitreception error values to audio device 34 related to the received data.Based upon these values, the transmitter DSP may undertake certain errorcorrection actions, including retransmission of bad data packets,adjustment of data packet size (e.g. transmit packets containing lessdata when the error rate is above a predetermined threshold, or adjustthe amount of data per packet dynamically as a function of the receptionerror rate), and increase of transmission power generated by IRtransmitter 18.

[0160] Referring now to FIG. 21, in an alternative embodiment vehicle900 includes communication system 901 according to the invention. Asdiscussed in connection with other embodiments, communication system 901may include audio device 34 hardwired through wire(s) 804 to phototransmitter/ receiver 806. As previously discussed, a communicationsystem according to the invention may include IR transmitter section 18to receive encoded data from audio device 34 and to control and powerphoto transmitter/receiver 806 to emit a digital bit stream of opticalpulses. IR transmitter section 18 may be provided separately from audiodevice 34 as shown in FIG. 18, for ease of installation, repair,maintenance, and upgrade, or may alternatively be included within audiodevice 34.

[0161] Audio device 34 may provide a plurality of channels of audio andother data, and is shown as receiving audio and video data from DVDplayer 803, audio and/or video data from auxiliary audio device 922(e.g. MP3 player, digital satellite radio tuner, video game player,etc.) and cellular telephone 805, geographical location data from GPSunit 920, and various vehicle data (e.g. telemetry information) from avehicle central processing unit (CPU) 924 that monitors and controlsvarious functions of vehicle 900. As previously described, acommunication system according to the invention may provide for two-waycommunications, and audio device 34 may thus also accept data receivedby transmitter/receiver 806 from other IR devices in vehicle 900 andchannel the data to such devices as vehicle CPU 924 and cellulartelephone 805. CPU 924 may receive information such as proximityinformation from video camera/proximity sensor 830 to display anappropriate video picture or a warning to the driver of vehicle 900.

[0162] With continued reference to FIG. 21, communication system 901 mayfurther include communication subsystem 921 including IRreceiver/transmitter 926 hardwired via wire(s) 827 to communicationmodule 923 that, as described elsewhere with connection to module 822(FIG. 17), may be hardwired to video camera/proximity sensor 830 toreceive data from the video camera and transmit it to vehicle CPU 924through IR receiver/transmitters 926, 806 and audio device 34. Module923 may also receive audio data from audio device 34 and provide theaudio data to subwoofer 942 that may be installed in the trunk or, asshown, underneath the rear seat of vehicle 900. Additionally, module 923may also be hardwired to trunk-mounted CD changer 950 and accept audiodata from the CD changer to transmit to audio device 34 for playbackwithin vehicle 900, as well as receive control commands input by thevehicle driver through audio device 34 to control the CD changer, suchas CD and track selection, shuffle, repeat, etc.

[0163] Module 923 may include one or more DACs to decode audio datareceived from audio device 34 as described elsewhere and convert thedecoded data to analog form for subwoofer 942. Alternatively, subwoofer942 may include a DAC and thus be able to accept decoded digital audiodata directly from module 923. Module 923 may also include one or moreADCs to accept analog data from video camera 830 and CD changer 950,convert it to digital form, encode it as described elsewhere herein, andtransmit it to audio device 34. As previously disclosed, a vehicle CPU924 may be connected to communication system 901, and system 901 may insuch an embodiment be used to relay telemetry and information related tothe vehicle to the CPU. For example, tire pressure monitor 952 may bedisposed in the rear area of vehicle 900 and may be hardwired to module923 to transmit information related to the rear tire(s) pressure tovehicle CPU 924. In this manner, the usefulness of communication system901 of the invention may be extended beyond entertainment functions tovehicle operational functions. In a further embodiment, IRreceiver/transmitter 926 may incorporate a repeater to receive IRsignals from any IR transmitters in vehicle 900, amplify the received IRsignals, and re-transmit the received signals for reception by other IRreceivers in the vehicle.

[0164] Wireless speaker 940 may be mounted in a door of vehicle 900 orat any other practicable location, and includes IR receiver/transmitter941. Preferably speaker 940 includes a DSP to decode encoded digitalaudio data received from IR receiver/transmitters 806, 926 and a DAC toconvert the decoded audio data to analog form for playback withinvehicle 900. Both speaker 940 and subwoofer 942 require a power source,which may be provided by the vehicle 900 power supply such as from thepower supply to the rear lights of the vehicle.

[0165] Still referring to FIG. 21, two-way headphones 980 include IRreceiver/transmitter 982 and microphone 984. IR receiver/transmitter 982communicates via an optical bit stream of data with audio device 34through IR receiver/transmitter 806 or, optionally, through IRreceiver/transmitter 926 that includes a repeater as describedpreviously. Two-way headphones 980 may be used to access cellulartelephone 805 through audio device 34 to place a call and conduct atwo-way conversation. Two-way headphones 980 may include a numeric padfor dialing, or alternatively audio device 34 may include voicerecognition capabilities to allow user 933 (using headphones 980) tosimply select a predetermined channel for placing telephone calls andthen activate and operate cellular telephone 805 by speaking commandsinto microphone 984. Two-way headphones 980 may further include an ADCconnected to microphone 984 to digitize the voice of user 933 forencoding and IR transmission as described elsewhere herein. Two-wayheadphones 980 preferably also provide the other functions provided byheadphones 80 as previously described, including controlling audiovolume and selecting one of a plurality of communication channels.

[0166] With continued reference to FIG. 21, remote controller 936includes IR receiver/transmitter 984 for two-way communication withaudio device 34 via IR receiver/transmitter 806 and, optionally, arepeater included in IR receiver/transmitter 926. Remote controller 936may provide any one or more of a plurality of controls, including butnot limited to key pads, joysticks, push buttons, toggles switches, andvoice command controls, and may further provide sensory feedback such asaudio or tactile/vibrations. Remote controller 936 may be used for avariety of purposes, including accessing and controlling cellulartelephone 805 as previously described. Remote controller 936 may also beused to access and control video game player 922 to play a video gamedisplayed on video display(s) 838, with the game audio track playedthrough headphones 80, 980. Remote controller 936 may further be used tocontrol video display 838 and adjust display functions and controls, tocontrol DVD player 803 to display a movie on video display 838 andcontrol its functions (e.g. pause, stop, fast forward), to controltrunk-mounted CD changer 950, to request telemetry data from vehicle CPU924 to display on video display 838, or to control other vehicle 900functions such as locking/unlocking doors and opening/closing windows.Two or more remote controllers 936 may be provided in vehicle 900 toallow two or more users 933, 935 to play a video game, displayedindividually on multiple, respective video displays 838. Each remotecontroller 936 may access audio device 34 and video game player 922through a separate communication channel and thus enable the game playerto provide different, individual video and audio streams to eachrespective user 933, 935 through the respective video displays 838 andheadphones 980, 80. Headphones 80, 980 may further be programmed toreceive an IR signal from remote controller 936 to select anotherchannel, or to automatically select the appropriate channel based uponthe function selected by the user (e.g. play a video game, watch a DVD).

[0167] In a further embodiment of the invention, DSP 76 of headphones 80may be programmed to identify different audio devices 34, such as may befound in a vehicle and in a home. Each audio device 34 may thus includefurther information in the header of each data packet to provide aunique identifier. DSP 76 may further include programmable memory tostore various user-selectable options related to each audio device 34from which the user of headphones 80 may wish to receive audio and otherdata. Thus, by way of example, DSP 76 may be programmed to receive anddecode a predetermined number of stereo and/or mono audio channels whenreceiving data from a vehicle-mounted audio device 34, and to receiveand decode six channels of mono audio data to provide a true 5.1 audioexperience when receiving data from an audio device 34 connected to ahome theatre system.

[0168] In another embodiment, headphones 80 operating according to theinvention may be provided with user customizable features, such as tonecontrols (e.g. bass, treble) that may be adjusted to different valuesfor each available channel, and which are automatically detected andapplied when the respective channel is selected by the user.Additionally, custom features may also be set for individual audiodevices 34, such an in-vehicle audio device and an in-home audio deviceas described above. Headphones 80 may therefore be provided withadditional controls such as bass and treble controls, and other signalprocessing options (e.g. panorama, concert hall, etc.). Custom settingsmay be retained as a headphone profile in a memory included withinheadphones 80, which may be any type of erasable memory. Alternatively,for two-way headphones 980, custom feature values adjusted by the usermay be transmitted to audio device 34 for storing in a memory within theaudio device, and these custom values may then be embedded in the datastream representing each channel (e.g. in the header of data packets) tobe recovered by headset 980 and applied to the signal of the selectedchannel.

[0169] Alternatively, custom features may be adjusted via audio device34 so that even one-way headphones 80 may enjoy customized settings. Inembodiments wherein customized features are stored in memory by audiodevice 34, each individual set of headphones 80 and/or 980 may beprovided with a means of individual identification, which may be enteredby a user via the controls provided on the headphones (e.g. define theheadphones as number one, two, three, etc.). The individualidentification will allow the audio device to embed the custom settingsfor every set of headphones in the data stream representing each channelto be recovered by each set of headphones, following which each set ofheadphones will identify and select its own appropriate set of customsettings to apply to the signal of the channel selected by the user ofthe particular set of headphones.

[0170] In addition to custom headset profiles, users may be allowed tospecify individual user profiles that specify the particular settingpreferences of each individual user of headphones within vehicle 900.Such individual profiles may be stored in audio device 34 andtransmitted within the data stream as described above. In thisembodiment, each user may be required to input a unique identifierthrough the controls of the selected headphones 80 to identify herselfto the headphones, which may be programmed to then extract theindividual user profile of the user wearing the headphones and applyingthe custom settings in the profile to the signal of the user selectedchannel. Such profiles may be embedded in each data packet, or may betransmitted only once when audio device 34 is first powered on, oralternatively may be transmitted at regular intervals. Alternatively,all user profiles may be stored in a memory by each set of headphones 80within a vehicle 900, and the profiles may updated intermittently orevery time upon power on of audio device 34.

[0171] With reference now to FIG. 22, in an alternative embodimentcommunication system 991 according to the invention is provided invehicle 988, wherein the vehicle includes data bus 990. Data bus 990 isconnected to vehicle CPU 924 and extends throughout vehicle 988 toconnect various devices (e.g. video camera 830, CD changer 950) withinthe vehicle to the CPU. Data bus 990 may extend through the headliner ofvehicle 988, as shown, or may take alternative paths through the vehicleto connected the desired devices. Data bus may be a fiber optic bus ormay be an electronic wired bus, and may operate at various transmissionspeeds and bandwidths. In one embodiment, data bus 990 may operateaccording to the Bluetooth wireless communications standard, or to theMedia Oriented Systems Transport (MOST) communications standard forfiber optic networks.

[0172] Communication system 991 includes IR modules 992 mounted at oneor more locations within vehicle 988 and connected to data bus 990. EachIR module 992 may contain an IR receiver (photoreceptor) and mayadditionally contain an IR transmitter (e.g. one or more LEDs). Aspreviously described, a repeater may also be incorporated into each IRmodule 992 to re-transmit received IR signals. Additionally, each IRmodule 992 includes circuitry (e.g. network interface card) forinterfacing with data bus 990 to read data being transmitted over thebus and convert the data to IR signals for transmission by the LED(s),and also to convert received IR signals to a data format accepted by thebus and transmit such data over the bus to audio device 34 or to anyother devices connected to the bus. The interface circuitry may furtherinclude a buffer or cache to buffer data if the IR receiver and/ortransmitter operate at a different speed from data bus 990.

[0173] In this embodiment, audio device 34 is not required to be thecentral control unit of communication system 991, which instead can be adistributed system wherein the IR modules 992 enable any IR deviceinside vehicle 988 to interface with any other IR device operatingaccording to the invention or with any other device that is connected todata bus 990. By properly addressing and identifying the datatransmitted over data bus 990 (e.g. via information placed in the headerof each data block or data packet), each device connected to the databus can identify the channel of data it is required to decode and use,and may optionally be assigned a unique address to which the data it isintended to receive can be uniquely addressed, in accordance with theprinciples of the invention set forth elsewhere herein (e.g. through theunique identifier ID described with reference to FIG. 10). This hybridnetwork is easily expandable as no additional wiring is needed toconnect additional devices to the network; instead, each new device canbe equipped with an IR transmitter/receiver that allows the device toconnect to the network through one of the wireless interfaces.

[0174] With reference now to FIG. 23, in yet another embodiment,communication system 1000 according to the invention is provided inbuilding 1010 wherein the building includes communication network 1020.Network 1020 may be a Local Area Network (LAN) that may be wired or maybe wireless, such as an 802.11 (WiFi) compliant wireless (RF) network.Alternatively, network 1020 may simply be a wired data pipelineconnected, for example, to local cable television company network 1022.As known in the art, network 1020 may thus interface with cable network1022 to receive media content such as television and music channels, andfurther to provide a connection to the Internet via cable modem 1024.

[0175] Network 1020 includes wireless (radio) RF transceiver 1030hardwired to the network and installed in room 1011 of building 1010 tobroadcast the data flowing on the network throughout the building via RFsignals 1032. To minimize RF interference throughout building 1010 frommultiple RF transmitters, room 1012 in the building may be equipped withinterface encoder/decoder 1040 connected to RF antenna 1034 to receiveRF signals 1032 from RF transmitter 1030 carrying data from network1020. Encoder/decoder 1040 may then encode the received network signalsas described elsewhere herein, e.g. in connection with the discussion ofFIG. 10, and drive an IR LED of IR transmitter/receiver 1050 to emit IRsignal 1052 carrying the network data. Devices in the room such as a PC1060 may be equipped with IR transmitter/receiver 1070 to receive IRsignal 1052 and encoder/decoder 1080 extract the data from the IRsignal, as well as to encode data from the PC and transmit it as IRsignal 1062 to be received by interface encoder/decoder 1040 throughtransmitter/receiver 1050. Interface encoder/decoder 1040 may thendecode or de-multiplex data carried by IR signal 1062 from PC 1060 andpass it on to RF antenna 1034, which in turn transmits the data as RFsignals 1036 to be received by transceiver 1030 and communicated tonetwork 1020.

[0176] With continued reference to FIG. 23, room 1013 of building 1010may be equipped with home theatre system 1100 connected to network 1020to receive television and audio programming. The home theatre system mayalso be connected to decoder 1110 to receive one or more channels ofaudio from a pre-amp of the home theatre system and drive IR transmitter1120 to transmit the channels of audio as IR signals 1122, as describedelsewhere herein. Devices in room 1012 such as wireless headphones 14and remote speakers 1130 may each be equipped with IR receivers 70 anddecoder circuitry for decoding IR signals 1122, as previously described.IR signals 1122 may carry audio information such as 5 channels ofmonaural audio for each speaker 1130 forming a so-called 5.1 audiosystem. IR signals may also carry multiple channels of audio such thatlistener 1150 wearing headphones 14 may choose to listen to a differentaudio channel than the channel being played by loudspeakers 1130. Itmust be understood that many other types of devices may be connectedwirelessly to network 1020 in the manner of the invention including, butnot limited to, telephones, facsimile machines, televisions, radios,video game consoles, personal digital assistants, various householdappliances equipped for remote control, and home security systems.

[0177] Hybrid system 1000 thus utilizes the ability of RF signals topropagate through walls, but minimizes the RF interference that mayarise in such situations. System 1000 is also highly flexible and allowsconnecting multiple additional devices, such as PC 1060, to a wirednetwork such as network 1020 without actually installing any additionalcable or wiring in the building. Instead, a single interfaceencoder/decoder 1040 needs to be installed in each room of the buildingand devices in any of the rooms so equipped can then be connected tonetwork 1020 through either a one-way decoder such as decoder 1110 or atwo-way encoder/decoder such as encoder/decoder 1080. In this manner,older buildings can be easily and cost-effectively retrofitted tobuilding modern offices with the requisite network/communicationcapabilities.

[0178] Having now described the invention in accordance with therequirements of the patent statutes, those skilled in this art willunderstand how to make changes and modifications to the presentinvention to meet their specific requirements or conditions. Suchchanges and modifications may be made without departing from the scopeand spirit of the invention as disclosed herein.

What is claimed is:
 1. A wireless transmission device for communicatinga plurality of audio streams to remote devices, comprising: a pluralityof inputs for receiving a plurality of digital audio streams; a combinerconnected to the inputs for combining control codes and the receivedaudio streams in a predetermined format to form a signal, the controlcodes for controlling the operation of a remote device equipped forprocessing the signal to extract the audio streams therefrom inaccordance with the predetermined format; and a transmitter connected tothe combiner to transmit the signal for reception by the remote device.2. The device of claim 1, further comprising: an analog input forreceiving an analog audio stream; and a converter connected to theanalog input for converting the received analog audio stream to adigital audio stream, the converter further connected to the combiner toprovide the converted digital audio stream to the combiner for combiningwith the control codes and the other received audio streams.
 3. Thedevice of claim 1, further comprising: one or more audio sourcesconnected to the inputs.
 4. The device of claim 3, wherein the audiosources are selected from the group of audio sources comprising compactdisc players, cassette tape players, radio tuners, telephones,televisions, computers, digital video disc players, mini-disc players,and MP3 -format and WMA-format digital players.
 5. The device of claim3, wherein the audio sources comprise: a in-dash stereo receiverconfigured for mounting in a vehicle dashboard.
 6. The device of claim2, further comprising: one or more audio sources connected to theinputs.
 7. The device of claim 6, wherein the audio sources are selectedfrom the group of audio sources comprising compact disc players,cassette tape players, radio tuners, telephones, televisions, computers,digital video disc players, mini-disc players, and MP3 -format andWMA-format digital players.
 8. The device of claim 6, wherein the audiosources comprise: a in-dash stereo receiver configured for mounting in avehicle dashboard.
 9. The device of claim 1, wherein the transmittercomprises: an infra-red light emitter for transmitting the signal as aninfra-red light signal.
 10. The device of claim 9, wherein the emittercomprises: one or more light-emitting diodes.
 11. The device of claim 1,further comprising: a connector connecting the combiner with thetransmitter.
 12. The device of claim 11, wherein the connectorcomprises: at least one wire for carrying the signal from the combinerto the transmitter.
 13. The device of claim 1, wherein the encodercomprises: at least one multiplexer for multiplexing the audio streams.14. The device of claim 13, wherein the encoder further comprises: adigital signal processor for combining the multiplexed audio streamswith the control codes in accordance with the predetermined format. 15.The device of claim 14, wherein the digital signal processor comprises:a digital signal processor for pulse position modulation of the signal.16. The device of claim 1, wherein the control codes comprise: controlcodes for detecting errors in the signal.
 17. The device of claim 1,wherein the control codes comprise: control codes for correcting errorsin the signal.
 18. The device of claim 1, wherein the control codescomprise: control codes for turning the remote device off.
 19. Thedevice of claim 1, wherein the control codes comprise: control codes forpowering the remote device down and powering the remote device up. 20.The device of claim 1, wherein the control codes comprise: control codesfor identifying the transmission device to the remote device.
 21. Thedevice of claim 1, wherein the control codes comprise: control codes foraffecting the signal processing performed by the remote device.
 22. Thedevice of claim 1, wherein the control codes comprise: control codes foridentifying the audio streams.
 23. The device of claim 1, wherein eachaudio stream comprises one or more channels of monaural sound.
 24. Thedevice of claim 22, wherein each audio stream is a stereophonic streamcomprising two channels of monaural sound.
 25. A wireless headphonedevice, comprising: a receiver for receiving a wireless signalcontaining a plurality of digital audio streams combined with controlcodes according to a predetermined format; a decoder for extracting theaudio streams from the received signal in accordance with thepredetermined format and for responding to the control codes in thereceived signal to perform predetermined functions; a selector forselecting one of the extracted audio streams; a converter for convertingthe selected audio stream to an analog audio stream; an amplifier foramplifying the converted analog audio stream; and a loudspeaker forreproducing the amplified audio stream.
 26. The device of claim 25,wherein the receiver comprises: a photoreceptor for receiving thewireless signal as an infrared light signal.
 27. The device of claim 26,wherein the decoder comprises: a demultiplexer to demultiplex thereceived signal and extract the audio streams from the demultiplexedsignal.
 28. The device of claim 27, wherein the decoder comprises: adecoder for responding to the control codes in the received signal todetect errors in the received signal.
 29. The device of claim 27,wherein the decoder comprises: a decoder for responding to the controlcodes in the received signal to correct errors in the received signal.30. The device of claim 27, wherein the decoder comprises: a decoder forresponding to the control codes in the received signal to turn thedevice off.
 31. The device of claim 27, wherein the decoder comprises: adecoder for responding to the control codes in the received signal topower the device down and power the device up.
 32. The device of claim27, wherein the decoder comprises: a decoder for responding to thecontrol codes in the received signal to identify the received signal.33. The device of claim 27, wherein the decoder comprises: a decoder forresponding to the control codes in the received signal to identify asource of the received signal.
 34. The device of claim 27, wherein thedecoder comprises: a decoder for responding to the control codes in thereceived signal to enable operation of the device upon identification ofa predetermined source.
 35. The device of claim 27, wherein the decodercomprises: a decoder for responding to the control codes in the receivedsignal to identify the audio streams in the received signal.
 36. Thedevice of claim 27, wherein the decoder comprises: a decoder forresponding to the control codes in the received signal to control theselector for selection of the channels available in the received signal.37. The device of claim 27, wherein the decoder comprises: a decoder forextracting audio streams, each audio stream comprising one or morechannels of monaural sound.
 38. The device of claim 27, wherein thedecoder comprises: a decoder for extracting audio streams, each audiostream comprising two channels of monaural sound.
 39. The device ofclaim 27, wherein the decoder comprises: a demultiplexer to demultiplexa pulse position modulated received signal.
 40. The device of claim 27,wherein the decoder comprises: a decoder for extracting synchronizationinformation from the received signal to synchronize with a source of thesignal.
 41. The device of claim 27, wherein the decoder comprises: acrystal oscillator selected to oscillate at a frequency of the source ofthe signal; and a pulse injector for responding to the received signalby generating synchronization pulses for the crystal oscillator tosynchronize the crystal oscillator to the frequency of the signalsource.